MICROALGAE FERMENTATION USING CONTROLLED ILLUMINATION
Bioreactors and methods for cultivating microalgae are provided herein. The bioreactor and methods include features and modifications to improve heterotrophic growth efficiency by providing a light signal.
This application claims the benefit of U.S. Provisional Application No. 61/243,593, filed Sep. 18, 2009, and U.S. Provisional Application No. 61/359,726, filed Jun. 29, 2010, the entire disclosures of which are hereby incorporated by reference in their entirety for all purposes.
FIELDThe invention relates to methods, means, and systems of fermentation of microorganisms, e.g., microalgae. The invention can be used in pharmaceutical, cosmetic and food industries, as well as for obtaining oil and biofuel from microalgae.
BACKGROUNDRecently, attention has been directed to the application of microalgae to the production of a variety of materials including lipids, hydrocarbons, oil, polysaccharides, pigments, and biofuels.
One of the conventional methods to grow microalgae is to heterotrophically culture it in an enclosed, light-free system. Techniques have been developed for the large-scale production of aquatic microalgae under heterotrophic growth conditions by utilizing organic carbon instead of light as an energy source. For example, U.S. Pat. Nos. 3,142,135 and 3,882,635 describe processes for the heterotrophic production of proteins and pigments from algae such as Chlorella, Spongiococcum, and Prototheca. In addition, heterotrophic algal cultures can attain much higher densities than photoautotrophic cultures.
However, the above application cannot be applied to all microalgae because only a limited number of microalgae strains can grow in heterotrophic conditions. Attempts to grow microalgae in heterotrophic conditions often involve either screening for strains that can grow in heterotrophic conditions or genetic modification of organisms to allow growth under such conditions.
Microalgae that contain both a proper transportation system for sugar and that can grow naturally in heterotrophic conditions often show slow growth rates or low production of materials of commercial interest since they have evolved many years to utilize sunlight as an environmental signal to control aspects of metabolism as well as energy generated through photosynthesis.
Most of the photosynthetic organisms, including microalgae, use light as an environmental signal to optimize themselves for growth and survival. Light signals are sensed by different photoreceptors including red/far-red photoreceptors (phytochromes) and blue light photoreceptors (cryptochromes and NPHs). Light serves as an environmental signal that regulates physiological and developmental processes and provides the energy that fuels the reduction of inorganic carbon. However, under certain conditions light also has the potential to be toxic. Photoinhibition occurs either when the photon flux absorbed by chloroplasts is very high (under high light conditions) or when the light energy influx exceeds the consumption capability (under mixotrophic conditions where a cell uses reduced carbon as an energy source). In mixotrophic conditions, photosynthetic organisms show photoinhibition at a much lower light intensity than autotrophic conditions since the electrons absorbed through the photosynthetic apparatus cannot be efficiently used due to a feedback mechanism in the Calvin cycle.
Absorbed light energy can result in the accumulation of excited chlorophyll molecules within the pigment bed and damage of the photosystem. Excited chlorophyll molecules that accumulate in the pigment bed as a consequence of excess excitation can also stimulate the production of active oxygen species such as superoxides, hydroxyl radicals and singlet oxygen.
SUMMARYDisclosed herein is a method for cultivating a microalgae capable of heterotrophic growth, including: incubating the microalgae under a heterotrophic growth condition for a period of time sufficient to allow the microalgae to grow, wherein the heterotrophic growth condition includes a media including a carbon source, and wherein the heterotrophic growth condition further includes a low irradiance of light.
In some embodiments, the microalgae is a Botryococcus strain, the carbon source is glucose, and the low irradiance of light is between 1-10 μmol photons m2 s−1.
In some embodiments, the microalgae is a Botryococcus sudeticus strain. In some embodiments, the microalgae is a Botryococcus strain. In some embodiments, the microalgae is a UTEX 2629 strain. In some embodiments, the microalgae is a Botryococcus braunii strain. In some embodiments, the microalgae is a UTEX 2441 strain. In some embodiments, the microalgae is a Neochloris oleabundans strain. In some embodiments, the microalgae is a Neochloris strain. In some embodiments, the microalgae is a UTEX 1185 strain. In some embodiments, the microalgae is a Chlamydomonas reinhardtii strain. In some embodiments, the microalgae is a Chlamydomonas strain. In some embodiments, the microalgae is a UTEX 2243 strain. In some embodiments, the microalgae comprises a photoreceptor.
In some embodiments, the carbon source is glucose. In some embodiments, the carbon source is selected from the group consisting of a fixed carbon source, glucose, fructose, sucrose, galactose, xylose, mannose, rhamnose, N-acetylglucosamine, glycerol, floridoside, glucuronic acid, corn starch, depolymerized cellulosic material, sugar cane, sugar beet, lactose, milk whey, and molasses.
In some embodiments, the light is produced by a natural light source. In some embodiments, the light is natural sun light. In some embodiments, the light comprises full spectrum light or a specific wavelength of light. In some embodiments, the light is produced by an artificial light source. In some embodiments, the light is artificial light. In some embodiments, the intensity of the low irradiance of light is between 0.01-1 μmol photons m−2 s−1. In some embodiments, the intensity of the low irradiance of light is between 1-10 μmol photons m−2 s−1. In some embodiments, the intensity of the low irradiance of light is between 10-100 μmol photons m−2 s−1. In some embodiments, the intensity of the low irradiance of light is between 100-300 μmol photons m−2 s−1. In some embodiments, the intensity of the low irradiance of light is between 100-300 μmol photons m−2 s−1. In some embodiments, the intensity of the low irradiance of light is 3-4 μmol/m2s1 photons, 2-3 μmol/m2s1 photons, 1-2 μmol/m2s−1 photons, or 3-5 μmol/m2s−1 photons.
In some embodiments, the method further includes producing a material from the microalgae. In some embodiments, the material is a polysaccharide, a pigment, a lipid, or a hydrocarbon. In some embodiments, the material is a hydrocarbon.
In some embodiments, the method further includes recovering the material. In some embodiments, the method further includes extracting the material.
In some embodiments, the method further includes processing the material. In some embodiments, the processing of the material produces a processed material. In some embodiments, the processed material is selected from the group consisting of a fuel, biodiesel, jet fuel, a cosmetic, a pharmaceutical agent, a surfactant, and a renewable diesel.
In some embodiments, the growth rate of the microalgae in the above methods is higher than a second microalgae incubated under a second heterotrophic growth condition for a period of time sufficient to allow the microalgae to grow, wherein the second heterotrophic growth condition includes a growth media comprising a carbon source, and wherein the second heterotrophic growth condition does not include a low irradiance of light.
Also described herein is a method of culturing microalgae, including placing a plurality of microalgae cells in the presence of a carbon source and a low irradiance of light.
Also described herein is a method of manufacturing a material, including: providing a microalgae capable of producing the material; culturing the microalgae in a media, wherein the media includes a carbon source; applying a low irradiance of light to the microalgae; and allowing the microalgae to accumulate at least 10% of its dry cell weight as the material. In some embodiments, the method further includes recovering the material.
Also described herein is a bioreactor system, including: a bioreactor; a culture media including a carbon source, wherein the culture media is located inside the bioreactor; a microalgae adapted for heterotrophic growth, wherein the microalgae is located in the culture media; and a light source, wherein the light source produces a low irradiance of light, and wherein the light source is operatively coupled to the bioreactor.
In some embodiments, light from the light source includes full spectrum light or a specific wavelength of light. In some embodiments, light from the light source includes natural sunlight collected by a solar energy collector operatively coupled to the bioreactor, and wherein the light is transmitted to the interior of the bioreactor through an optical fiber operatively coupled to the solar collector and the bioreactor. In some embodiments, light from the light source includes artificial light, wherein the artificial light is produced by a light emitted diode (LED) or a fluorescent light. In some embodiments, the system further includes a power supply sufficient to power the LED or fluorescent light, wherein the power supply is operatively coupled to the bioreactor; and a light controller operatively coupled to the power supply, wherein the light controller is adapted to control the intensity and wavelength of light emitted by the LED or fluorescent light. In some embodiments, the optical fibre is mounted in a transparent and protective light structure. In some embodiments, the LED is mounted in a transparent and protective light structure.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, and accompanying drawings, where:
Terms used in the claims and specification are defined as set forth below unless otherwise specified.
“Axenic” means a culture of an organism that is free from contamination by other living organisms.
“Biodiesel” is a biologically produced fatty acid alkyl ester suitable for use as a fuel in a diesel engine.
The term “biomass” refers to material produced by growth and/or propagation of cells. Biomass may contain cells and/or intracellular contents as well as extracellular material. Extracellular material includes, but is not limited to, compounds secreted by a cell.
“Bioreactor” means an enclosure or partial enclosure in which cells are cultured, optionally in suspension.
As used herein, a “catalyst” refers to an agent, such as a molecule or macromolecular complex, capable of facilitating or promoting a chemical reaction of a reactant to a product without becoming a part of the product. A catalyst thus increases the rate of a reaction, after which, the catalyst may act on another reactant to form the product. A catalyst generally lowers the overall activation energy required for the reaction such that it proceeds more quickly or at a lower temperature. Thus reaction equilibrium may be more quickly attained. Examples of catalysts include enzymes, which are biological catalysts, heat, which is a non-biological catalyst, and metal catalysts used in fossil oil refining processes.
“Cellulosic material” means the products of digestion of cellulose, including glucose and xylose, and optionally additional compounds such as disaccharides, oligosaccharides, lignin, furfurals and other compounds. Nonlimiting examples of sources of cellulosic material include sugar cane bagasses, sugar beet pulp, corn stover, wood chips, sawdust and switchgrass.
The term “co-culture”, and variants thereof such as “co-cultivate”, refer to the presence of two or more types of cells in the same bioreactor. The two or more types of cells may both be microorganisms, such as microalgae, or may be a microalgal cell cultured with a different cell type. The culture conditions may be those that foster growth and/or propagation of the two or more cell types or those that facilitate growth and/or proliferation of one, or a subset, of the two or more cells while maintaining cellular growth for the remainder.
The term “cofactor” is used herein to refer to any molecule, other than the substrate, that is required for an enzyme to carry out its enzymatic activity.
The term “cultivated”, and variants thereof, refer to the intentional fostering of growth (increases in cell size, cellular contents, and/or cellular activity) and/or propagation (increases in cell numbers via mitosis) of one or more cells by use of intended culture conditions. The combination of both growth and propagation may be termed proliferation. The one or more cells may be those of a microorganism, such as microalgae. Examples of intended conditions include the use of a defined medium (with known characteristics such as pH, ionic strength, and carbon source), specified temperature, oxygen tension, carbon dioxide levels, and growth in a bioreactor. The term does not refer to the growth or propagation of microorganisms in nature or otherwise without direct human intervention, such as natural growth of an organism that ultimately becomes fossilized to produce geological crude oil.
As used herein, the term “cytolysis” refers to the lysis of cells in a hypotonic environment. Cytolysis is caused by excessive osmosis, or movement of water, towards the inside of a cell (hyperhydration). The cell cannot withstand the osmotic pressure of the water inside, and so it explodes.
As used herein, the terms “expression vector” or “expression construct” refer to a nucleic acid construct, generated recombinantly or synthetically, with a series of specified nucleic acid elements that permit transcription of a particular nucleic acid in a host cell. The expression vector can be part of a plasmid, virus, or nucleic acid fragment. Typically, the expression vector includes a nucleic acid to be transcribed operably linked to a promoter.
“Exogenous gene” refers to a nucleic acid transformed into a cell. A transformed cell may be referred to as a recombinant cell, into which additional exogenous gene(s) may be introduced. The exogenous gene may be from a different species (and so heterologous), or from the same species (and so homologous) relative to the cell being transformed. In the case of a homologous gene, it occupies a different location in the genome of the cell relative to the endogenous copy of the gene. The exogenous gene may be present in more than one copy in the cell. The exogenous gene may be maintained in a cell as an insertion into the genome or as an episomal molecule.
“Exogenously provided” describes a molecule provided to the culture media of a cell culture.
“Fixed carbon source” means molecule(s) containing carbon, e.g. organic, that are present at ambient temperature and pressure in solid or liquid form.
“Homogenate” means biomass that has been physically disrupted.
As used herein, “hydrocarbon” refers to: (a) a molecule containing only hydrogen and carbon atoms wherein the carbon atoms are covalently linked to form a linear, branched, cyclic, or partially cyclic backbone to which the hydrogen atoms are attached; or (b) a molecule that only primarily contains hydrogen and carbon atoms and that can be converted to contain only hydrogen and carbon atoms by one to four chemical reactions. Nonlimiting examples of the latter include hydrocarbons containing an oxygen atom between one carbon and one hydrogen atom to form an alcohol molecule, as well as aldehydes containing a single oxygen atom. Methods for the reduction of alcohols to hydrocarbons containing only carbon and hydrogen atoms are well known. Another example of a hydrocarbon is an ester, in which an organic group replaces a hydrogen atom (or more than one) in an oxygen acid. The molecular structure of hydrocarbon compounds varies from the simplest, in the form of methane (CH4), which is a constituent of natural gas, to the very heavy and very complex, such as some molecules such as asphaltenes found in crude oil, petroleum, and bitumens. Hydrocarbons may be in gaseous, liquid, or solid form, or any combination of these forms, and may have one or more double or triple bonds between adjacent carbon atoms in the backbone. Accordingly, the term includes linear, branched, cyclic, or partially cyclic alkanes, alkenes, lipids, and paraffin. Examples include propane, butane, pentane, hexane, octane, triolein, and squalene.
The term “hydrogen:carbon ratio” refers to the ratio of hydrogen atoms to carbon atoms in a molecule on an atom-to-atom basis. The ratio may be used to refer to the number of carbon and hydrogen atoms in a hydrocarbon molecule. For example, the hydrocarbon with the highest ratio is methane CH4 (4:1).
“Hydrophobic fraction” refers to the portion, or fraction, of a material that is more soluble in a hydrophobic phase in comparison to an aqueous phase. A hydrophobic fraction is substantially insoluble in water and usually non-polar.
As used herein, the phrase “increase lipid yield” refers to an increase in the productivity of a microbial culture by, for example, increasing dry weight of cells per liter of culture, increasing the percentage of cells that constitute lipid, or increasing the overall amount of lipid per liter of culture volume per unit time.
An “inducible promoter” is one that mediates transcription of an operably linked gene in response to a particular stimulus.
As used herein, the phrase “in operable linkage” refers to a functional linkage between two sequences, such a control sequence (typically a promoter) and the linked sequence. A promoter is in operable linkage with an exogenous gene if it can mediate transcription of the gene.
The term “in situ” means “in place” or “in its original position”. For example, a culture may contain a first microalga secreting a catalyst and a second microorganism secreting a substrate, wherein the first and second cell types produce the components necessary for a particular chemical reaction to occur in situ in the co-culture without requiring further separation or processing of the materials.
A “limiting concentration of a nutrient” is a concentration in a culture that limits the propagation of a cultured organism. A “non-limiting concentration of a nutrient” is a concentration that supports maximal propagation during a given culture period. Thus, the number of cells produced during a given culture period is lower in the presence of a limiting concentration of a nutrient than when the nutrient is non-limiting. A nutrient is said to be “in excess” in a culture, when the nutrient is present at a concentration greater than that which supports maximal propagation.
As used herein, a “lipase” is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water-insoluble, lipid substrates. Lipases catalyze the hydrolysis of lipids into glycerols and fatty acids.
“Lipids” are a class of hydrocarbon that are soluble in nonpolar solvents (such as ether and chloroform) and are relatively or completely insoluble in water. Lipid molecules have these properties because they consist largely of long hydrocarbon tails which are hydrophobic in nature. Examples of lipids include fatty acids (saturated and unsaturated); glycerides or glycerolipids (such as monoglycerides, diglycerides, triglycerides or neutral fats, and phosphoglycerides or glycerophospholipids); nonglycerides (sphingolipids, sterol lipids including cholesterol and steroid hormones, prenol lipids including terpenoids, fatty alcohols, waxes, and polyketides); and complex lipid derivatives (sugar-linked lipids, or glycolipids, and protein-linked lipids). “Fats” are a subgroup of lipids called “triacylglycerides.”
The term “low irradiance of light” refers to the irradiance of light that can be applied to a microorganism while avoiding significant photoinhibition under heterotrophic conditions and the irradiance of light needed to initiate a light-activated metabolism in the microorganism. Light-activated metabolisms include, but are not limited to, a life cycle, a circadian rhythm, cell division, a biosynthetic pathway, and a transport system.
As used herein, the term “lysate” refers to a solution containing the contents of lysed cells.
As used herein, the term “lysis” refers to the breakage of the plasma membrane and optionally the cell wall of a biological organism sufficient to release at least some intracellular content, often by mechanical, viral or osmotic mechanisms that compromise its integrity.
As used herein, the term “lysing” refers to disrupting the cellular membrane and optionally the cell wall of a biological organism or cell sufficient to release at least some intracellular content.
“Microalgae” means a eukaryotic microbial organism that contains a chloroplast, and optionally that is capable of performing photosynthesis, or a prokaryotic microbial organism capable of performing photosynthesis. Microalgae include obligate photoautotrophs, which cannot metabolize a fixed carbon source as energy, as well as heterotrophs, which can live solely off of a fixed carbon source. Microalgae can refer to unicellular organisms that separate from sister cells shortly after cell division, such as Chlamydomonas, and can also refer to microbes such as, for example, Volvox, which is a simple multicellular photosynthetic microbe of two distinct cell types. “Microalgae” can also refer to cells such as Chlorella and Dunaliella. “Microalgae” also includes other microbial photosynthetic organisms that exhibit cell-cell adhesion, such as Agmenellum, Anabaena, and Pyrobotrys. “Microalgae” also includes obligate heterotrophic microorganisms that have lost the ability to perform photosynthesis, such as certain dinoflagellate algae species. Other examples of microalgae are described below.
The terms “microorganism” and “microbe” are used interchangeably herein to refer to microscopic unicellular organisms, e.g., microalgae.
As used herein, the term “osmotic shock” refers to the rupture of cells in a solution following a sudden reduction in osmotic pressure. Osmotic shock is sometimes induced to release cellular components of such cells into a solution.
“Polysaccharides” (also called “glycans”) are carbohydrates made up of monosaccharides joined together by glycosidic linkages. Cellulose is an example of a polysaccharide that makes up certain plant cell walls. Cellulose can be depolymerized by enzymes to yield monosaccharides such as xylose and glucose, as well as larger disaccharides and oligosaccharides.
“Port”, in the context of a bioreactor, refers to an opening in the bioreactor that allows influx or efflux of materials such as gases, liquids, and cells. Ports are usually connected to tubing leading from the bioreactor.
A “promoter” is defined as an array of nucleic acid control sequences that direct transcription of a nucleic acid. As used herein, a promoter includes necessary nucleic acid sequences near the start site of transcription, such as, in the case of a polymerase II type promoter, a TATA element. A promoter also optionally includes distal enhancer or repressor elements, which can be located as much as several thousand base pairs from the start site of transcription.
As used herein, the term “recombinant” when used with reference, e.g., to a cell, or nucleic acid, protein, or vector, indicates that the cell, nucleic acid, protein or vector, has been modified by the introduction of an exogenous nucleic acid or protein or the alteration of a native nucleic acid or protein, or that the cell is derived from a cell so modified. Thus, e.g., recombinant cells express genes that are not found within the native (non-recombinant) form of the cell or express native genes that are otherwise abnormally expressed, under expressed or not expressed at all. By the term “recombinant nucleic acid” herein is meant nucleic acid, originally formed in vitro, in general, by the manipulation of nucleic acid, e.g., using polymerases and endonucleases, in a form not normally found in nature. In this manner, operably linkage of different sequences is achieved. Thus an isolated nucleic acid, in a linear form, or an expression vector formed in vitro by ligating DNA molecules that are not normally joined, are both considered recombinant for the purposes of this invention. It is understood that once a recombinant nucleic acid is made and reintroduced into a host cell or organism, it will replicate non-recombinantly, i.e., using the in vivo cellular machinery of the host cell rather than in vitro manipulations; however, such nucleic acids, once produced recombinantly, although subsequently replicated non-recombinantly, are still considered recombinant for the purposes of the invention. Similarly, a “recombinant protein” is a protein made using recombinant techniques, i.e., through the expression of a recombinant nucleic acid as depicted above.
As used herein, the term. “renewable diesel” refers to alkanes (such as C:10:0, C12:0, C:14:0, C16:0 and C18:0) produced through hydrogenation and deoxygenation of lipids.
As used herein, the term “sonication” refers to a process of disrupting biological materials, such as a cell, by use of sound wave energy.
“Species of furfural” refers to 2-Furancarboxaldehyde or a derivative thereof which retains the same basic structural characteristics.
As used herein, “stover” refers to the dried stalks and leaves of a crop remaining after a grain has been harvested.
“Wastewater” is watery waste which typically contains washing water, laundry waste, feces, urine and other liquid or semi-liquid wastes. It includes some forms of municipal waste as well as secondarily treated sewage.
It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.
Microorganisms
Any species of organism that produces suitable lipid or hydrocarbon can be used, although microorganisms that naturally produce high levels of suitable lipid or hydrocarbon are preferred. Production of hydrocarbons by microorganisms is reviewed by Metzger et al. Appl Microbiol Biotechnol (2005) 66: 486-496 and A Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae, NREL/TP-580-24190, John Sheehan, Terri Dunahay, John Benemann and Paul Roessler (1998).
Considerations affecting the selection of microorganisms for use in the invention include, in addition to production of suitable lipids or hydrocarbons for production of oils, fuels, and oleochemicals, include: (1) high lipid content as a percentage of cell weight; (2) ease of growth; (3) ease of genetic engineering; and (4) ease of biomass processing. In particular embodiments, the wild-type or genetically engineered microorganism yields cells that are at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, or at least 70% or more lipid. Preferred organisms grow heterotrophically or can be engineered to do so using, for example, methods disclosed herein. The ease of transformation and availability of selectable markers and promoters, constitutive and/or inducible, that are functional in the microorganism affect the ease of genetic engineering. Processing considerations can include, for example, the availability of effective means for lysing the cells.
In one embodiment, microorganisms include natural or engineered microorganisms that can grow under heterotrophic condition and use tight as signal to control cellular processes. These can include alga such as Cyanophyta, Chlorophyta, Rhodophyta, Cryptophyta, Chlorarachniophyta, Haptophyta, Euglenophyta, Heterokontophyta, and Diatoms.
Algae
In one embodiment of the present invention, the microorganism is a microalgae. Nonlimiting examples of microalgae that can be used in accordance with the present invention are described below.
More specifically, algal taxa belonging to the Cyanophyta, including Cyanophyceae, are those being Prokaryotae, which have the ability of oxygen evolution-type photosynthesis and are classified into the following orders and families. Chroococcales include Microcystaceae, Chroococcaceae, Entophysalidaceae, Chamaesiphoniaceae, Dermocarpellaceae, Xenococcaceae, and Hydrococcaceae, Oscillatoriales includes Borziaceae, Pseudanabaenaceae, Schizotrichaceae, Phormidiaceae, Oscillatoriaceae, and Homoeotrichaceae, Nostocales includes Scytonemataceae, Microchaetaceae, Rivulariaceae, and Nostocaceae, and Stigonematales includes Chlorogloeopsaceae, Capsosiraceae, Stigonemataceae, Fischerellaceae Borzinemataceae, Nostochopsaceae, and Mastigocladaceae.
Chlorophyta include Chlorophyceae, Prasinophyceae, Pedinophyceae, Trebouxiophyceae, and Ulvophyceae. More specifically, Chlorophyceae includes Acetabularia, Acicularia, Actinochloris, Amphikrikos, Anadyomene, Ankistrodesmus, Ankyra, Aphanochaete, Ascochloris, Asterococcus, Asteromonas, Astrephomene, Atractomorpha, Axilococcus, Axilosphaera, Basichlamys, Basicladia, Binuclearia, Bipedinomonas, Blastophysa, Boergesenia, Boodlea, Borodinella, Borodinellopsis, Botryococcus, Brachiomonas, Bracteacoccus, Bulbochaete, Caespitella, Capsosiphon, Carteria, Centrosphaera, Chaetomorpha, Chaetonema, Chaetopeltis, Chaetophora, Chalmasia, Chamaetrichon, Characiochloris, Characiosiphon, Characium, Chlamydella, Chlamydobotrys, Chlamydocapsa, Chlamydomonas, Chlamydopodium, Chloranomala, Chlorochydridion, Chlorochytrium, Chlorocladus, Chlorocloster, Chlorococcopsis, Chlorococcum, Chlorogonium, Chloromonas, Chlorophysalis, Chlorosarcina, Chlorosarcinopsis, Chlorosphaera, Chlorosphaeropsis, Chlorotetraedron, Chlorothecium, Chodatella, Choricystis, Cladophora, Cladophoropsis, Cloniophora, Closteriopsis, Coccobotrys, Coelastrella, Coelastropsis, Coelastrum, Coenochloris, Coleochlamys, Coronastrum, Crucigenia, Crucigeniella, Ctenocladus, Cylindrocapsa, Cylindrocapsopsis, Cylindrocystis, Cymopolia, Cystococcus, Cystomonas, Dactylococcus, Dasycladus, Deasonia, Derbesia, Desmatractum, Desmodesmus, Desmotetra, Diacanthos, Dicellula, Dicloster, Dicranochaete, Dictyochloris, Dictyococcus, Dictyosphaeria, Dictyosphaerium, Didymocystis, Didymogenes, Dilabifilum, Dimorphococcus, Diplosphaera, Draparnaldia, Dunaliella, Dysmorphococcus, Echinocoleum, Elakatothrix, Enallax, Entocladia, Entransia, Eremosphaera, Ettlia, Eudorina, Fasciculochloris, Fernandinella, Follicularia, Fottea, Franceia, Friedmannia, Fritschiella, Fusola, Geminella, Gloeococcus, Gloeocystis, Gloeodendron, Gloeomonas, Gloeotila, Golenkinia, Gongrosira, Gonium, Graesiella, Granulocystis, Gyorffiana, Haematococcus, Hazenia, Helicodictyon, Hemichloris, Heterochlamydomonas, Heteromastix, Heterotetracystis, Hormidiospora, Hormidium, Hormotila, Hormotilopsis, Hyalococcus, Hyalodiscus, Hyalogonium, Hyaloraphidium, Hydrodictyon, Hypnomonas, Ignatius, Interfilum, Kentrosphaera, Keratococcus, Kermatia, Kirchneriella, Koliella, Lagerheimia, Lautosphaeria, Leptosiropsis, Lobocystis, Lobomonas, Lola, Macrochloris, Marvania, Micractinium, Microdictyon, Microspora, Monoraphidium, Muriella, Mychonastes, Nanochlorum, Nautococcus, Neglectella, Neochloris, Neodesmus, Neomeris, Neospongiococcum, Nephrochlamys, Nephrocytium, Nephrodiella, Oedocladium, Oedogonium, Oocystella, Oocystis, Oonephris, Ourococcus, Pachycladella, Palmella, Palmellococcus, Palmellopsis, Palmodictyon, Pandorina, Paradoxia, Parietochloris, Pascherina, Paulschulzia, Pectodictyon, Pediastrum, Pedinomonas, Pedinopera, Percursaria, Phacotus, Phaeophila, Physocytium, Pilina, Planctonema, Planktosphaeria, Platydorina, Platymonas, Pleodorina, Pleurastrum, Pleurococcus, Ploeotila, Polyedriopsis, Polyphysa, Polytoma, Polytomella, Prasinocladus, Prasiococcus, Protoderma, Protosiphon, Pseudendocloniopsis, Pseudocharacium, Pseudochlorella, Pseudochlorococcum, Pseudococcomyxa, Pseudodictyosphaerium, Pseudodidymocystis, Pseudokirchneriella, Pseudopleurococcus, Pseudoschizomeris, Pseudoschroederia, Pseudostichococcus, Pseudotetracystis, Pseudotetradron, Pseudotrebouxia, Pteromonas, Pulchrasphaera, Pyramimonas, Pyrobotrys, Quadrigula, Radiofilum, Radiosphaera, Raphidocelis, Raphidonema, Raphidonemopsis, Rhizoclonium, Rhopalosolen, Saprochaete, Scenedesmus, Schizochlamys, Schizomeris, Schroederia, Schroederiella, Scotiellopsis, Siderocystopsis, Siphonocladus, Sirogonium, Sorastrum, Spermatozopsis, Sphaerella, Sphaerellocystis, Sphaerellopsis, Sphaerocystis, Sphaeroplea, Spirotaenia, Spongiochloris, Spongiococcum, Stephanoptera, Stephanosphaera, Stigeoclonium, Struvea, Tetmemorus, Tetrabaena, Tetracystis, Tetradesmus, Tetraedron, Tetrallantos, Tetraselmis, Tetraspora, Tetrastrum, Treubaria, Triploceros, Trochiscia, Trochisciopsis, Ulva, Uronema, Valonia, Valoniopsis, Ventricaria, Viridiella, Vitreochlamys, Volvox, Volvulina, Westella, Willea, Wislouchiella, Zoochlorella, Zygnemopsis, Hyalotheca, Chlorella, Pseudopleurococcum and Rhopalocystis. Prasinophyceae includes Heteromastix, Mammella, Mantoniella, Micromonas, Nephroselmis, Ostreococcus, Prasinocladus, Prasinococcus, Pseudoscourfielda, Pycnococcus, Pyramimonas, Scherffelia. Pedinophyceae includes Marsupiomonas, Pedinomonas, Resultor. Trebouxiophyceae includes Apatococcus, Asterochloris, Auxenochlorella, Chlorella, Coccomyxa, Desmococcus, Dictyochloropsis, Elliptochloris, Jaagiella, Leptosira, Lobococcus, Makinoella, Microthamnion, Myrmecia, Nannochloris, Oocystis, Prasiola, Prasiolopsis, Prototheca, Stichococcus, Tetrachlorella, Trebouxia, Trichophilus, Watanabea and Myrmecia. Ulvophyceae includes Acrochaete, Bryopsis, Cephaleuros, Chlorocystis, Enteromorpha, Gloeotilopsis, Halochlorococcum, Ostreobium, Pirula, Pithophora, Planophila, Pseudendoclonium, Trentepohlia, Trichosarcina, Ulothrix, Bolbocoleon, Chaetosiphon, Eugomontia, Oltmannsiellopsis, Pringsheimiella, Pseudodendroclonium, Pseudulvella, Sporocladopsis, Urospora, and Wittrockiella.
Rhodophyta include Acrochaetium, Agardhiella, Antithamnion, Antithamnionella, Asterocytis, Andouinella, Balbiania, Bangia, Batrachospermum, Bonnemaisonia, Bostrychia, Callithamnion, Caloglossa, Ceramium, Champia, Chroodactylon, Chroothece, Compsopogon, Compsopogonopsis, Cumagloia, Cyanidium, Cystoclonium, Dasya, Digenia, Dixoniella, Erythrocladia, Erythrolobas, Erythrotrichia, Flintiella, Galdieria, Gelidium, Glaucosphaera, Goniotrichum, Gracilaria, Grateloupia, Griffithsia, Hildenbrandia, Hymenocladiopsis, Hypnea, Laingia, Membranoptera, Myriogramme, Nemalion, Nemnalionopsis, Neoagardhiella, Palmaria, Phyllophora, Polyneura, Polysiphonia, Porphyra, Porphyridium, Pseudochantransia, Pterocladia, Pugetia, Rhodella, Rhodochaete, Rhodochorton, Rhodosorus, Rhodospora, Rhodymenia, Seirospora, Selenastrum, Sirodotia, Solieria, Spermothamnion, Spyridia, Stylonema, Thorea, Trailiella and Tuomeya.
Cryptophyta include Cryptophyceae. More specifically, Campylomonas, Chilomonas, Chroomonas, Cryptochrysis, Cryptomonas, Goniomonas, Guillardia, Hanusia, Hemiselmis, Plagioselmis, Proteomonas, Pyrenomonas, Rhodomonas and Stroreatula.
Chlorarachniophyta include Chlorarachnion, Lotharella and Chattonella.
Haptophyta include Apistonema, Chrysochromulina, Coccolithophora, Corcontochrysis, Cricosphaera, Diacronema, Emiliana, Pavlova, Ruttnera, Cruciplacolithus, Prymnesium, Isochrysis, Calyptrosphaera, Chrysotila, Coccolithus, Dicrateria, Heterosigma, Hymenomonas, Imantonia, Gephyrocapsa, Ochrosphaera, Phaeocystis, Platychrysis, Pseudoisochrysis, Syracosphaera and Pleurochrysis.
Euglenophyta include stasia, Colacium, Cyclidiopsis, Distigma, Euglena, Eutreptia, Eutreptiella, Gyropaigne, Hyalophacus, Khawkinea Astasia, Lepocinclis, Menoidium, Parmidium, Phacus, Rhabdomonas, Rhabdospira, Tetruetreptia and Trachelomonas.
Heterokontophyta include Bacillariophyceae, Phaeophyceae, Pelagophyceae, Xanthophyceae, Eustigmatophyceae, Syanurophyceae, Phaeothamniophyceae and Raphidophyceae. More specifically, Bacillariophyceae includes Achnanthes, Amphora, Chaetoceros, Bacillaria, Nitzschia, Navicula, and Pinnularia. Phaeophyceae includes Ascoseira, Asterocladon, Bodanella, Desmarestia, Dictyocha, Dictyota, Ectocarpus, Halopteris, Heribaudiella, Pleurocladia, Porterinema, Pylaiella, Sorocarpus, Spermatochnus, Sphacelaria and Waerniella. Pelagophyceae includes Aureococcus, Aureoumbra, Pelagococcus, Pelagomonas, Pulvinaria and Sarcinochrysis. Xanthophyceae includes Chloramoebales, Rhizochloridales, Mischococcales, Tribonematales, and Vaucheriales. Eustigmatophyceae includes Chloridella, Ellipsoidion, Eustigmatos, Monodopsis, Monodus, Nannochloropsis, Polyedriella, Pseudocharaciopsis, Pseudostaurastrum and Vischeria Syanurophyceae includes allomonas, Synura and Tessellaria. Phaeothamniophyceae includes haeobotrys and Phacothamnion. Raphidophyceae includes Olisthodiscus, Vacuolaria and Fibrocapsa.
Diatoms include Bolidophyceae, Coscinodiscophyceae, Dinophyceae and Alveolates. Bolidophyceae include Bolidomonas, Chrysophyceae, Giraudyopsis, Glossomastix, Chromophyton, Chrysamoeba, Chrysochaete, Chrysodidymus, Chrysolepidomonas, Chrysosaccus, Chrysosphaera, Chrysoxys, Cyclonexis, Dinobryon, Epichrysis, Epipyxis, Hibberdia, Lagynion, Lepochromulina, Monas, Monochrysis, Paraphysomonas, Phacoplaca, Phacoschizochlamys, Picophagus, Pleurochrysis, Stichogloca and Uroglena. Coscinodiscophyceae include Bacteriastrum, Bellerochea, Biddulphia, Brockmanniella, Corethron, Coscinodiscus, Eucampia, Extubocellulus, Guinardia, Helicotheca, Leptocylindrus, Leyanella, Lithodesmium, Melosira, Minidiscus, Odentella, Planktoniella, Porosira, Proboscia, Rhizosolenia, Stellarima, Thalassionema, Bicosoecid, Symbiomonas, Actinocyclus, Amphora, Arcocellulus, Detonula, Diatoma, Ditylum, Fragilariophyceae, Asterionellopsis, Delphineis, Grammatophora, Nanofrustulum, Synedra and Tabularia. Dinophyceae includes Adenoides, Alexandrium, Amphidinium, Ceratium, Ceratocorys, Coolia, Crypthecodinium, Exuviaella, Gambierdiscus, Gonyaulax, Gymnodinium, Gyrodinium, Heterocapsa, Katodinium, Lingulodinium, Pfiesteria, Polarella, Protoceratium, Pyrocystis, Scrippsiella, Symbiodinium, Thecadinium, Thoracosphaera, and Zooxanthella. Alveolates include Cystodinium, Glenodinium, Oxyrrhis, Peridinium, Prorocentrum, and Woloszynskia.
Methods of Culturing Microorganisms and Bioreactors
Microorganisms are generally cultured both for purposes of conducting genetic manipulations and for subsequent production of hydrocarbons (e.g., lipids, fatty acids, aldehydes, alcohols, and alkanes). The former type of culture is generally conducted on a small scale and initially, at least, under conditions in which the starting microorganism can grow. Culture for purposes of hydrocarbon production is usually conducted on a large scale. Preferably a fixed carbon source (e.g. a feedstock) is present. The culture can also be exposed to light some or all of the time.
Bioreactor
Microalgae can be cultured in liquid media. The culture can be contained within a bioreactor. Microalgae can also be cultured in photobioreactors that contain a fixed carbon source and allow light to strike the cells. Exposure of microalgae cells to light, even in the presence of a fixed carbon source that the cells transport and utilize, can accelerate growth compared to culturing cells in the dark. Culture condition parameters can be manipulated to optimize total hydrocarbon production, the combination of hydrocarbon species produced, and/or production of a hydrocarbon species.
In one aspect, a bioreactor is a fermentation tank used for industrial fermentation processes.
In some embodiments, a bioreactor includes glass, metal or plastic tanks, equipped with, e.g., gauges and settings to control aeration, stir rate, temperature, pH, and other parameters of interest. Generally the gauges and settings are operatively coupled to the bioreactor.
In one aspect, a bioreactor can be small enough for bench-top applications (5-10 L or less) or up to 120,000 L or larger in capacity for large-scale industrial applications.
In some embodiments, the bioreactor system can include a light-diffusing structure or a plurality of light-diffusing structures. In some embodiments, one or more of the light-diffusing structures from the plurality of light-diffusing structures are located along the interior surface of the bioreactor. In some embodiments, the light-diffusing structure is operatively coupled to the bioreactor.
The bioreactor system can include one or more optical fibers and/or a plurality of light sources and/or a light source. In some embodiments, the one or more optical fibres are mounted in protective and optically transparent lighting structures. In some embodiments, the optical fiber is operatively coupled to the bioreactor. In some embodiments, the light source is operatively coupled to the bioreactor.
In some embodiments, the bioreactor system can include a lighting structure operatively coupled to a bioreactor. In certain embodiments herein a lighting structure can have any shape or form as it directs light signal to the interior of a bioreactor. The bioreactor system may also include at least one optical fiber extending from a first end of at least one of the one or more optical fibers to a portion of a solar energy collector. In some embodiments, the solar energy collector is operatively coupled to the bioreactor. The optical fiber can be adapted to optically couple the solar energy collector to the bioreactor. The optical fiber may be optically coupled (directly or indirectly) to the solar energy collector.
In some embodiments, the bioreactor system includes a plurality of light sources operatively coupled to the bioreactor. The plurality of light sources can include multiple LEDs. The plurality of light sources comprising multiple LEDs can be operable to supply full spectrum or a specific wavelength of artificial light to a bioreactor.
In one embodiment, an LED is mounted in protective and optically transparent lighting structures. In one embodiment the LED is an array of LEDs.
In some embodiments, microalgae can be grown and maintained in closed bioreactors made of different types of transparent or semitransparent material. Such material can include Plexiglass™ enclosures, glass enclosures, bags made from substances such as polyethylene, transparent or semitransparent pipes, and other materials. Microalgae can be grown and maintained in open bioreactors such as raceway ponds, settling ponds, and other non-enclosed containers.
The gas content of a bioreactor to grow microorganisms like microalgae can be manipulated. Part of the volume of a bioreactor can contain gas rather than liquid. Gas inlets can be used to pump gases into the bioreactor. Any gas can be pumped into a bioreactor, including air, air/O2 mixtures, noble gases such as argon and others. The rate of entry of gas into a bioreactor can also be manipulated. Increasing gas flow into a bioreactor increases the turbidity of a culture of microalgae. Placement of ports conveying gases into a bioreactor can also affect the turbidity of a culture at a given gas flow rate. Air/O2 mixtures can be modulated to generate optimal amounts of O2 for maximal growth by a particular organism. Microalgae grow significantly faster in the light under, for example, 3% O2/97% air than in 100% air. 3% O2/97% air is approximately 100-fold more O2 than found in air. For example, air:O2 mixtures of about 99.75% air:0.25% O2, about 99.5% air:0.5% O2, about 99.0% air:1.00% O2, about 98.0% air:2.0% O2, about 97.0% air:3.0% O2, about 96.0% air:4.0% O2, and about 95.00% air:5.0% O2 can be infused into a bioreactor or bioreactor.
Microalgae cultures can also be subjected to mixing using devices such as spinning blades and impellers, rocking of a culture, stir bars, infusion of pressurized gas, and other instruments.
Bioreactors can have ports allowing entry of gases, solids, semisolids and liquids into the chamber containing the microalgae. Ports are usually attached to tubing or other means of conveying substances. Gas ports, for example, convey gases into the culture. Pumping gases into a bioreactor can serve to both feed cells O2 and other gases and to aerate the culture and therefore generate turbidity. The amount of turbidity of a culture varies as the number and position of gas ports is altered. For example, gas ports can be placed along the boftom of a cylindrical polyethylene bag. Microalgae grow faster when O2 is added to air and bubbled into a bioreactor.
Bioreactors preferably have one or more ports that allow media entry. It is not necessary that only one substance enter or leave a port. For example, a port can be used to flow culture media into the bioreactor and then later can be used for sampling, gas entry, gas exit, or other purposes. In some instances a bioreactor is filled with culture media at the beginning of a culture and no more growth media is infused after the culture is inoculated. In other words, the microalgal biomass is cultured in an aqueous medium for a period of time during which the microalgae reproduce and increase in number; however quantities of aqueous culture medium are not flowed through the bioreactor throughout the time period. Thus in some embodiments, aqueous culture medium is not flowed through the bioreactor after inoculation.
In other instances culture media can be flowed though the bioreactor throughout the time period during which the microalgae reproduce and increase in number. In some embodiments media is infused into the bioreactor after inoculation but before the cells reach a desired density. In other words, a turbulent flow regime of gas entry and media entry is not maintained for reproduction of microalgae until a desired increase in number of said microalgae has been achieved.
Bioreactors preferably have one or more ports that allow gas entry. Gas can serve to both provide nutrients such as O2 as well as to provide turbulence in the culture media. Turbulence can be achieved by placing a gas entry port below the level of the aqueous culture media so that gas entering the bioreactor bubbles to the surface of the culture. One or more gas exit ports allow gas to escape, thereby preventing pressure buildup in the bioreactor. Preferably a gas exit port leads to a “one-way” valve that prevents contaminating microorganisms from entering the bioreactor. In some instances cells are cultured in a bioreactor for a period of time during which the microalgae reproduce and increase in number, however a turbulent flow regime with turbulent eddies predominantly throughout the culture media caused by gas entry is not maintained for all of the period of time. In other instances a turbulent flow regime with turbulent eddies predominantly throughout the culture media caused by gas entry can be maintained for all of the period of time during which the microalgae reproduce and increase in number. In some instances a predetermined range of ratios between the scale of the bioreactor and the scale of eddies is not maintained for the period of time during which the microalgae reproduce and increase in number. In other instances such a range can be maintained.
Bioreactors preferably have at least one port that can be used for sampling the culture. Preferably a sampling port can be used repeatedly without altering compromising the axenic nature of the culture. A sampling port can be configured with a valve or other device that allows the flow of sample to be stopped and started. Alternatively a sampling port can allow continuous sampling. Bioreactors preferably have at least one port that allows inoculation of a culture. Such a port can also be used for other purposes such as media or gas entry.
In one embodiment, a bioreactor with an irradiation system can be used to produce hydrocarbon from Botryococcus. Botryococcenes are unbranched isoprenoid triterpenes having the formula CnH2n-10. The A race produces alkadienes and alkatrienes (derivatives of fatty acids) wherein n is an odd number 23 through 31. The B race produces botryococcenes wherein n is in the range 30 through 40. These can be biofuels of choice for hydrocracking to gasoline-type hydrocarbons.
Media
Microalgal culture media typically contains components such as a fixed nitrogen source, trace elements, optionally a buffer for pH maintenance, and phosphate. Other components can include a fixed carbon source such as acetate or glucose, and salts such as sodium chloride, particularly for seawater microalgae. Examples of trace elements include zinc, boron, cobalt, copper, manganese, and molybdenum in, for example, the respective forms of ZnCl2, H3BO3, CoCl2.6H2O, CuCl2.2H2O, MnCl2.4H2O and (NH4)6Mo7O24.4H2O.
For organisms able to grow on a fixed carbon source, the fixed carbon source can be, for example, glucose, fructose, sucrose, galactose, xylose, mannose, rhamnose, N-acetylglucosamine, glycerol, floridoside, and/or glucuronic acid. The one or more carbon source(s) can be supplied at a concentration of less than 50 μM, at least about 50 μM, at least about 100 μM, at least about 500 μM, at least about 5 mM, at least about 50 mM, at least about 500 mM, and more than 500 mM of one or more exogenously provided fixed carbon source(s). The one or more carbon source(s) can be supplied at a less than 1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of the media. The one or more carbon source(s) can also be supplied at a percentage of the media between the above noted percentages, e.g., 2.5% or 3.7% of the media.
Some microorganisms naturally grow on or can be engineered to grow on a fixed carbon source that is a heterogeneous source of compounds such as municipal waste, secondarily treated sewage, wastewater, and other sources of fixed carbon and other nutrients such as sulfates, phosphates, and nitrates. The sewage component serves as a nutrient source in the production of hydrocarbons, and the culture provides an inexpensive source of hydrocarbons.
Other culture parameters can also be manipulated, such as the pH of the culture media, the identity and concentration of trace elements and other media constituents.
Microorganisms useful in accordance with the methods of the present invention are found in various locations and environments throughout the world. As a consequence of their isolation from other species and their resulting evolutionary divergence, the particular growth medium for optimal growth and generation of lipid and/or hydrocarbon constituents can vary. In some cases, certain strains of microorganisms may be unable to grow on a particular growth medium because of the presence of some inhibitory component or the absence of some essential nutritional requirement required by the particular strain of microorganism.
Solid and liquid growth media are generally available from a wide variety of sources, and instructions for the preparation of particular media that is suitable for a wide variety of strains of microorganisms can be found, for example, online at a site maintained by the University of Texas at Austin for its culture collection of algae (UTEX).
Process conditions can be adjusted to increase the yield of lipids suitable for a particular use and/or to reduce production cost. For example, in certain embodiments, a microbe (e.g., microalgae) is cultured in the presence of a limiting concentration of one or more nutrients, such as, for example, carbon and/or nitrogen, phosphorous, or sulfur, while providing an excess of fixed carbon energy such as glucose. Nitrogen limitation tends to increase microbial lipid yield over microbial lipid yield in a culture in which nitrogen is provided in excess. In particular embodiments, the increase in lipid yield is at least about: 10%, 20%, 30%, 40%, 50%, 75%, 100%, 200%, 300%, 400%, or 500%. The microbe can be cultured in the presence of a limiting amount of a nutrient for a portion of the total culture period or for the entire period. In particular embodiments, the nutrient concentration is cycled between a limiting concentration and a non-limiting concentration at least twice during the total culture period.
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- Heterotrophic Growth and Light
Microorganisms can be cultured under heterotrophic growth conditions in which a fixed carbon source provides energy for growth and lipid accumulation.
Standard methods for the heterotrophic growth and propagation of microalgae are known (see for example Miao and Wu, J Biotechnology, 2004, 11:85-93 and Miao and Wu, Biosource Technology (2006) 97:841-846).
For hydrocarbon production, cells, including recombinant cells of the invention described herein, can be cultured or fermented in large quantities. The culturing may be in large liquid volumes, such as in suspension cultures as an example. Other examples include starting with a small culture of cells which expand into a large biomass in combination with cell growth and propagation as well as hydrocarbon production. Bioreactors or steel fermentors can be used to accommodate large culture volumes. A bioreactor can include a fermentor. A fermentor similar those used in the production of beer and/or wine can be suitable, as are extremely large fermentors used in the production of ethanol.
Appropriate nutrient sources for culture in a fermentor are provided. These include raw materials such as one or more of the following: a fixed carbon source such as glucose, corn starch, depolymerized cellulosic material, sucrose, sugar cane, sugar beet, lactose, milk whey, or molasses; a fat source, such as fats or vegetable oils; a nitrogen source, such as protein, soybean meal, cornsteep liquor, ammonia (pure or in salt form), nitrate or nitrate salt, or molecular nitrogen; and a phosphorus source, such as phosphate salts. Additionally, a fermentor allows for the control of culture conditions such as temperature, pH, oxygen tension, and carbon dioxide levels. Optionally, gaseous components, like oxygen or nitrogen, can be bubbled through a liquid culture. Other Starch (glucose) sources such as wheat, potato, rice, and sorghum. Other carbon sources include process streams such as technical grade glycerol, black liquor, organic acids such as acetate, and molasses. Carbon sources can also be provided as a mixture, such as a mixture of sucrose and depolymerized sugar beet pulp.
A fermentor can be used to allow cells to undergo the various phases of their growth cycle. As an example, an inoculum of hydrocarbon-producing cells can be introduced into a medium followed by a lag period (lag phase) before the cells begin growth. Following the lag period, the growth rate increases steadily and enters the log, or exponential, phase. The exponential phase is in turn followed by a slowing of growth due to decreases in nutrients and/or increases in toxic substances. After this slowing, growth stops, and the cells enter a stationary phase or steady state, depending on the particular environment provided to the cells.
Hydrocarbon production by cells disclosed herein can occur during the log phase or thereafter, including the stationary phase wherein nutrients are supplied, or still available, to allow the continuation of hydrocarbon production in the absence of cell division.
Preferably, microorganisms grown using conditions described herein and known in the art comprise at least about 20% by weight of lipid, preferably at least about 40% by weight, more preferably at least about 50% by weight, and most preferably at least about 60% by weight.
In an alternate heterotrophic growth method in accordance with the present invention, microorganisms can be cultured using depolymerized cellulosic biomass as a feedstock. Cellulosic biomass (e.g., stover, such as corn stover) is inexpensive and readily available; however, attempts to use this material as a feedstock for yeast have failed. In particular, such feedstock has been found to be inhibitory to yeast growth, and yeast cannot use the 5-carbon sugars produced from cellulosic materials (e.g., xylose from hemi-cellulose). By contrast, microalgae can grow on processed cellulosic material. Accordingly, the invention provides a method of culturing microalgae in the presence of a cellulosic material and/or a 5-carbon sugar.
Suitable cellulosic materials include residues from herbaceous and woody energy crops, as well as agricultural crops, i.e., the plant parts, primarily stalks and leaves, not removed from the fields with the primary food or fiber product. Examples include agricultural wastes such as sugarcane bagasse, rice hulls, corn fiber (including stalks, leaves, husks, and cobs), wheat straw, rice straw, sugar beet pulp, citrus pulp, citrus peels; forestry wastes such as hardwood and softwood thinnings, and hardwood and softwood residues from timber operations; wood wastes such as saw mill wastes (wood chips, sawdust) and pulp mill waste; urban wastes such as paper fractions of municipal solid waste, urban wood waste and urban green waste such as municipal grass clippings; and wood construction waste. Additional cellulosics include dedicated cellulosic crops such as switchgrass, hybrid poplar wood, and miscanthus, fiber cane, and fiber sorghum. Five-carbon sugars that are produced from such materials include xylose.
In still another alternative heterotrophic growth method in accordance with the present invention, which itself may optionally be used in combination with the methods described above, sucrose, produced by example from sugar cane or sugar beet, is used as a feedstock.
Heterotrophic growth can include the use of both light and fixed carbon source(s) for cells to grow and produce hydrocarbons. Heterotrophic growth can be conducted in a photobioreactor.
Bioreactors can be exposed to one or more light sources to provide microalgae with a light signal. A light signal can be provided via light directed to a surface of the bioreactor by a light source. Preferably the light source provides an intensity that is sufficient for the cells to grow, but not so intense as to cause oxidative damage or cause a photoinhibitive response. In some instances a light source has a wavelength range that mimics or approximately mimics the range of the sun. In other instances a different wavelength range is used. Bioreactors can be placed outdoors or in a greenhouse or other facility that allows sunlight to strike the surface. In some embodiments, photon intensities for species of the genus Botryococcus are between 25 and 500 μmE m−2 s−1 (see for example Photosynth Res. 2005 June; 84(1-3):21-7).
The number of photons striking a culture of microalgae cells can be manipulated, as well as other parameters such as the wavelength spectrum and ratio of dark:light hours per day. Microalgae can also be cultured in natural light, as well as simultaneous and/or alternating combinations of natural light and artificial light. For example, microalgae can be cultured under natural light during daylight hours and under artificial light during night hours.
In one aspect of the invention, a microorganism is exposed to about 0.1% to about 1% of light irradiance required for photosynthesis, preferably about 0.3% to about 0.8% of light irradiance required for photosynthesis by the organism. Typical light irradiance can be between 0.1-300 μmol photons m−2 s−1 including less than 0.1, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 to 99, 100, 101 to 149, 150, 151, to 199, 200, 201 to 249, 250, or greater than 250 μmol photons m−2 s−1. Light irradiance can be about 0.01-1 μmol photons m−2 s−1, preferably between 1-10 μmol photons m−2 s−1, or between 10-100 μmol photons m−2 s−1, or between 100-300 μmol photons m−2 s−1, or between 100-300 μmol photons m−2 s−1. Also included are light irradiances between the above noted light irradiances, e.g., 1.1, 2.1, 2.5, or 3.5 μmol photons m−2 s−1.
In one aspect, different light spectrums (e.g. 360-700 nm) can be used. Light spectrums can be less than 300, 300, 350, 400, 450, 500, 550, 600, 650, 700, or 750 nm or more. Also included are light spectrums between the above noted light spectrums, e.g., 360 or 440 nm.
In one embodiment, the irradiation can be applied in a continuous manner. In another embodiment, the irradiation can be applied in a cyclic pattern with an appropriate period of lighting including but not limited to 12 h light:12 h dark or 16 h light:8 h dark. Light patterns can include less than 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 h of light and/or less than 1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23 hours (h) of dark. Also included are light patterns between the above noted light patterns, e.g., 7.5 h of light or 7.5 h of dark.
In one embodiment, the irradiation can be natural sunlight collected by a solar collector and transmitted to the interior of a bioreactor through an optical fiber.
In another embodiment, artificial light, such as light emitted diodes (LEDs) or fluorescent light can be used as light source. In another embodiment, natural sunlight and artificial light can be used together.
In one embodiment, the irradiation is a full spectrum of light.
In another embodiment, the irradiation is a specific wavelength of light or a range of spectrum light transmitted through a specific filter.
Methods of Recovering Lipids and Hydrocarbons
Hydrocarbons (e.g., lipids, fatty acids, aldehydes, alcohols, and alkanes) produced by cells of the invention can be harvested, or otherwise collected, by any convenient means. For example, hydrocarbons secreted from cells can be centrifuged to separate the hydrocarbons in a hydrophobic layer from contaminants in an aqueous layer and optionally from any solid materials as a precipitate in after centrifugation. Material containing cell or cell fractions can be treated with proteases to degrade contaminating proteins before or after centrifugation. In some instances the contaminating proteins are associated, possibly covalently, to hydrocarbons or hydrocarbon precursors which form hydrocarbons upon removal of the protein. In other instances the hydrocarbon molecules are in a preparation that also contains proteins. Proteases can be added to hydrocarbon preparations containing proteins to degrade proteins (for example, the protease from Streptomyces griseus can be used (SigmaAldrich catalog number P5147). After digestion, the hydrocarbons are preferably purified from residual proteins, peptide fragments, and amino acids. This purification can be accomplished, for example, by methods listed above such as centrifugation and filtration.
Extracellular hydrocarbons can also be extracted in vivo from living microalgae cells which are then returned to a bioreactor by exposure of the cells, in an otherwise sterile environment, to a non-toxic extraction solvent, followed by separation of the living cells and the hydrophobic fraction of extraction solvent and hydrocarbons, wherein the separated living cells are then returned to a culture container such as a stainless steel fermentor or photobioreactor (see Biotechnol Bioeng. 2004 Dec. 5; 88(5):593-600 and Biotechnol Bioeng. 2004 Mar. 5; 85(5):475-81).
Hydrocarbons can also be isolated by whole cell extraction. The cells are first disrupted and then intracellular and cell membrane/cell wall-associated hydrocarbons as well as extracellular hydrocarbons can be collected from the whole cell mass, such as by use of centrifugation as described above.
Various methods are available for separating hydrocarbons and lipids from cellular lysates produced by the above methods. For example, hydrocarbons can be extracted with a hydrophobic solvent such as hexane (see Frenz et al. 1989, Enzyme Microb. Technol., 11:717). Hydrocarbons can also be extracted using liquefaction (see for example Sawayama et al. 1999, Biomass and Bioenergy 17:33-39 and Inoue et al. 1993, Biomass Bioenergy 6(4):269-274); oil liquefaction (see for example Minowa et al. 1995, Fuel 74(12):1735-1738); and supercritical CO2 extraction (see for example Mendes et al. 2003, Inorganica Chimica Acta 356:328-334).
Miao and Wu describe a protocol of the recovery of microalgal lipid from a culture in which the cells were harvested by centrifugation, washed with distilled water and dried by freeze drying. The resulting cell powder was pulverized in a mortor and then extracted with n-hexane. Miao and Wu, Biosource Technology (2006) 97:841-846.
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- Lysing Cells
Intracellular lipids and hydrocarbons produced in microorganisms are, in some embodiments, extracted after lysing the cells of the microorganism. Once extracted, the lipids and/or hydrocarbons can be further refined to produce, e.g., oils, fuels, or oleochemicals.
After completion of culturing, the microorganisms can be separated from the fermentation broth. Optionally, the separation is effected by centrifugation to generate a concentrated paste. Centrifugation does not remove significant amounts of intracellular water from the microorganisms and is not a drying step. The biomass can then be washed with a washing solution (e.g., DI water) to get rid of the fermentation broth and debris. Optionally, the washed microbial biomass may also be dried (oven dried, lyophilized, etc.) prior to cell disruption. Alternatively, cells can be lysed without separation from some or all of the fermentation broth when the fermentation is complete. For example, the cells can be at a ratio of less than 1:1 v:v cells to extracellular liquid when the cells are lysed.
Microorganisms containing a lipid and/or hydrocarbon can be lysed to produce a lysate. As detailed herein, the step of lysing a microorganism (also referred to as cell lysis) can be achieved by any convenient means, including heat-induced lysis, adding a base, adding an acid, using enzymes such as proteases and polysaccharide degradation enzymes such as amylases, using ultrasound, mechanical lysis, using osmotic shock, infection with a lytic virus, and/or expression of one or more lytic genes. Lysis is performed to release intracellular molecules which have been produced by the microorganism. Each of these methods for lysing a microorganism can be used as a single method or in combination simultaneously or sequentially.
The extent of cell disruption can be observed by microscopic analysis. Using one or more of the methods described herein, typically more than 70% cell breakage is observed. Preferably, cell breakage is more than 80%, more preferably more than 90% and most preferred about 100%.
In particular embodiments, the microorganism is lysed after growth, for example to increase the exposure of cellular lipid and/or hydrocarbon for extraction or further processing. The timing of lipase expression (e.g., via an inducible promoter) or cell lysis can be adjusted to optimize the yield of lipids and/or hydrocarbons. Below are described a number of lysis techniques. These techniques can be used individually or in combination.
Heat-Induced Lysis
In a preferred embodiment of the present invention, the step of lysing a microorganism comprises heating of a cellular suspension containing the microorganism. In this embodiment, the fermentation broth containing the microorganisms (or a suspension of microorganisms isolated from the fermentation broth) is heated until the microorganisms, i.e., the cell walls and membranes of microorganisms degrade or breakdown. Typically, temperatures applied are at least 50 C. Higher temperatures, such as, at least 30 C, at least 60 C, at least 70 C, at least 80 C, at least 90 C, at least 100 C, at least 110 C, at least 120 C, at least 130 C or higher are used for more efficient cell lysis.
Lysing cells by heat treatment can be performed by boiling the microorganism. Alternatively, heat treatment (without boiling) can be performed in an autoclave. The heat treated lysate may be cooled for further treatment.
Cell disruption can also be performed by steam treatment, i.e., through addition of pressurized steam. Steam treatment of microalgae for cell disruption is described, for example, in U.S. Pat. No. 6,750,048.
Lysis Using a Base
In another preferred embodiment of the present invention, the step of lysing a microorganism comprises adding a base to a cellular suspension containing the microorganism.
The base should be strong enough to hydrolyze at least a portion of the proteinaceous compounds of the microorganisms used. Bases which are useful for solubilizing proteins are known in the art of chemistry. Exemplary bases which are useful in the methods of the present invention include, but are not limited to, hydroxides, carbonates and bicarbonates of lithium, sodium, potassium, calcium, and mixtures thereof. A preferred base is KOH. Base treatment of microalgae for cell disruption is described, for example, in U.S. Pat. No. 6,750,048.
Acidic Lysis
In another preferred embodiment of the present invention, the step of lysing a microorganism comprises adding an acid to a cellular suspension containing the microorganism. Acid lysis can be affected using an acid at a concentration of 10-500 mN or preferably 40-160 nM. Acid lysis is preferably performed at above room temperature (e.g., at 40-160, and preferably a temperature of 50-130. For moderate temperatures (e.g., room temperature to 100 C and particularly room temperature to 65, acid treatment can usefully be combined with sonication or other cell disruption methods.
Lysing Cells Using Enzymes
In another preferred embodiment of the present invention, the step of lysing a microorganism comprises lysing the microorganism by using an enzyme. Preferred enzymes for lysing a microorganism are proteases and polysaccharide-degrading enzymes such as hemicellulase (e.g., hemicellulase from Aspergillus niger; Sigma Aldrich, St. Louis, Mo.; #H2125), pectinase (e.g., pectinase from Rhizopus sp.; Sigma Aldrich, St. Louis, Mo.; #P2401), Mannaway 4.0 L (Novozymes), cellulase (e.g., cellulose from Trichoderma viride; Sigma Aldrich, St. Louis, Mo.; #C9422), and driselase (e.g., driselase from Basidiomycetes sp.; Sigma Aldrich, St. Louis, Mo.; #D9515.
Cellulases
In a preferred embodiment of the present invention, a cellulase for lysing microorganism is a polysaccharide-degrading enzyme, optionally from Chlorella or a Chlorella virus.
Proteases
Proteases such as Streptomyces griseus protease, chymotrypsin, proteinase K, proteases listed in Degradation of Polylactide by Commercial Proteases, Oda Y et al., Journal of Polymers and the Environment, Volume 8, Number 1, January 2000, pp. 29-32(4), and other proteases can be used to lyse microorganisms. Other proteases that can be used include Alcalase 2.4 FG (Novozymes) and Flavourzyme 100 L (Novozymes).
Combinations
Any combination of a protease and a polysaccharide-degrading enzyme can also be used, including any combination of the preceding proteases and polysaccharide-degrading enzymes.
Lysing Cells Using Ultrasound
In another preferred embodiment of the present invention, the step of lysing a microorganism is performed by using ultrasound, i.e., sonication. Thus, cells can also by lysed with high frequency sound. The sound can be produced electronically and transported through a metallic tip to an appropriately concentrated cellular suspension. This sonication (or ultrasonication) disrupts cellular integrity based on the creation of cavities in cell suspension.
Mechanical Lysis
In another preferred embodiment of the present invention, the step of lysing a microorganism is performed by mechanical lysis. Cells can be lysed mechanically and optionally homogenized to facilitate hydrocarbon (e.g., lipid) collection. For example, a pressure disrupter can be used to pump a cell containing slurry through a restricted orifice valve. High pressure (up to 1500 bar) is applied, followed by an instant expansion through an exiting nozzle. Cell disruption is accomplished by three different mechanisms: impingement on the valve, high liquid shear in the orifice, and sudden pressure drop upon discharge, causing an explosion of the cell. The method releases intracellular molecules.
Alternatively, a ball mill can be used. In a ball mill, cells are agitated in suspension with small abrasive particles, such as beads. Cells break because of shear forces, grinding between beads, and collisions with beads. The beads disrupt the cells to release cellular contents. Cells can also be disrupted by shear forces, such as with the use of blending (such as with a high speed or Waring blender as examples), the french press, or even centrifugation in case of weak cell walls, to disrupt cells.
Lysing Cells by Osmotic Shock (Cytolysis)
In another preferred embodiment of the present invention, the step of lysing a microorganism is performed by applying an osmotic shock.
Infection with a Lytic Virus
In a preferred embodiment of the present invention, the step of lysing a microorganism comprises infection of the microorganism with a lytic virus. A wide variety of viruses are known to lyse microorganisms suitable for use in the present invention, and the selection and use of a particular lytic virus for a particular microorganism is within the level of skill in the art.
For example, paramecium bursaria chlorella virus (PBCV-1) is the prototype of a group (family Phycodnaviridae, genus Chlorovirus) of large, icosahedral, plaque-forming, double-stranded DNA viruses that replicate in, and lyse, certain unicellular, eukaryotic chlorella-like green algae. Accordingly, any susceptible microalgae can be lysed by infecting the culture with a suitable chlorella virus. See for example Adv. Virus Res. 2006; 66:293-336; Virology, 1999 Apr. 25; 257(1):15-23; Virology, 2004 Jan. 5; 318(1):214-23; Nucleic Acids Symp. Ser. 2000; (44):161-2; J. Virol. 2006 March; 80(5):2437-44; and Annu. Rev. Microbiol. 1999; 53:447-94.
Autolysis (Expression of a Lytic Gene)
In another preferred embodiment of the present invention, the step of lysing a microorganism comprises autolysis. In this embodiment, a microorganism according to the invention is genetically engineered to produce a lytic protein that will lyse the microorganism. This lytic gene can be expressed using an inducible promoter so that the cells can first be grown to a desirable density in a fermentor, followed by induction of the promoter to express the lytic gene to lyse the cells. In one embodiment, the lytic gene encodes a polysaccharide-degrading enzyme.
In certain other embodiments, the lytic gene is a gene from a lytic virus. Thus, for example, a lytic gene from a Chlorella virus can be expressed in an algal cell of the genus Chlorella, such as C. protothecoides.
Suitable expression methods are described herein with respect to the expression of a lipase gene. Expression of lytic genes is preferably done using an inducible promoter, such as a promoter active in microalgae that is induced by a stimulus such as the presence of a small molecule, light, heat, and other stimuli. For example, see Virology 260, 308-315 (1999); FEMS Microbiology Letters 180 (1999) 45-53; Virology 263, 376-387 (1999); and Virology 230, 361-368 (1997).
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- Extraction of Lipids and Hydrocarbons
Lipids and hydrocarbons generated by the microorganisms of the present invention can be recovered by extraction with an organic solvent. In some cases, the preferred organic solvent is hexane. Typically, the organic solvent is added directly to the lysate without prior separation of the lysate components. In one embodiment, the lysate generated by one or more of the methods described above is contacted with an organic solvent for a period of time sufficient to allow the lipid anchor hydrocarbon components to form a solution with the organic solvent. In some cases, the solution can then be further refined to recover specific desired lipid or hydrocarbon components. Hexane extraction methods are well known in the art.
Methods of Processing Lipids and Hydrocarbons
Enzymatic Modification
Hydrocarbons (e.g., lipids, fatty acids, aldehydes, alcohols, and alkanes) produced by cells as described herein can be modified by the use of one or more enzymes, including a lipase. When the hydrocarbons are in the extracellular environment of the cells, the one or more enzymes can be added to that environment under conditions in which the enzyme modifies the hydrocarbon or completes its synthesis from a hydrocarbon precursor. Alternatively, the hydrocarbons can be partially, or completely, isolated from the cellular material before addition of one or more catalysts such as enzymes. Such catalysts are exogenously added, and their activity occurs outside the cell or in vitro.
Thermal and Other Catalytic Modification
Hydrocarbons produced by cells in vivo, or enzymatically modified in vitro, as described herein can be optionally further processed by conventional means. The processing can include “cracking” to reduce the size, and thus increase the hydrogen:carbon ratio, of hydrocarbon molecules. Catalytic and thermal cracking methods are routinely used in hydrocarbon and triglyceride oil processing. Catalytic methods involve the use of a catalyst, such as a solid acid catalyst. The catalyst can be silica-alumina or a zeolite, which result in the heterolytic, or asymmetric, breakage of a carbon-carbon bond to result in a carbocation and a hydride anion. These reactive intermediates then undergo either rearrangement or hydride transfer with another hydrocarbon. The reactions can thus regenerate the intermediates to result in a self-propagating chain mechanism. Hydrocarbons can also be processed to reduce, optionally to zero, the number of carbon-carbon double, or triple, bonds therein. Hydrocarbons can also be processed to remove or eliminate a ring or cyclic structure therein. Hydrocarbons can also be processed to increase the hydrogen:carbon ratio. This can include the addition of hydrogen (“hydrogenation”) and/or the “cracking” of hydrocarbons into smaller hydrocarbons.
Thermal methods involve the use of elevated temperature and pressure to reduce hydrocarbon size. An elevated temperature of about 800 C and pressure of about 700 kPa can be used. These conditions generate “light,” a term that is sometimes used to refer to hydrogen-rich hydrocarbon molecules (as distinguished from photon flux), while also generating, by condensation, heavier hydrocarbon molecules which are relatively depleted of hydrogen. The methodology provides homolytic, or symmetrical, breakage and produces alkenes which may be optionally enzymatically saturated as described above.
Catalytic and thermal methods are standard in plants for hydrocarbon processing and oil refining. Thus hydrocarbons produced by cells as described herein can be collected and processed or refined via conventional means. See Hillen et al. (Biotechnology and Bioengineering, Vol. XXIV: 193-205 (1982)) for a report on hydrocracking of microalgae-produced hydrocarbons. In alternative embodiments, the fraction is treated with another catalyst, such as an organic compound, heat, and/or an inorganic compound. For processing of lipids into biodiesel, a transesterification process is used as described in Section IV herein.
Hydrocarbons produced via methods of the present invention are useful in a variety of industrial applications. For example, the production of linear alkylbenzene sulfonate (LAS), an anionic surfactant used in nearly all types of detergents and cleaning preparations, utilizes hydrocarbons generally comprising a chain of 10-14 carbon atoms. See, for example, U.S. Pat. Nos. 6,946,430; 5,506,201; 6,692,730; 6,268,517; 6,020,509; 6,140,302; 5,080,848; and 5,567,359. Surfactants, such as LAS, can be used in the manufacture of personal care compositions and detergents, such as those described in U.S. Pat. Nos. 5,942,479; 6,086,903; 5,833,999; 6,468,955; and 6,407,044.
Methods of Producing Fuels Suitable for Use in Diesel Vehicles and Jet Engines
Increasing interest is directed to the use of hydrocarbon components of biological origin in fuels, such as biodiesel, renewable diesel, and jet fuel, since renewable biological starting materials that may replace stalling materials derived from fossil fuels are available, and the use thereof is desirable. There is a need for methods for producing hydrocarbon components from biological materials. The present invention fulfills this need by providing methods for production of biodiesel, renewable diesel, and jet fuel using the lipids generated by the methods described herein as a biological material to produce biodiesel, renewable diesel, and jet fuel.
Traditional diesel fuels are petroleum distillates rich in paraffinic hydrocarbons. They have boiling ranges as broad as 370 to 780 F, which are suitable for combustion in a compression ignition engine, such as a diesel engine vehicle. The American Society of Testing and Materials (ASTM) establishes the grade of diesel according to the boiling range, along with allowable ranges of other fuel properties, such as cetane number, cloud point, flash point, viscosity, aniline point, sulfur content, water content, ash content, copper strip corrosion, and carbon residue. Technically, any hydrocarbon distillate material derived from biomass or otherwise that meets the appropriate ASTM specification can be defined as diesel fuel (ASTM D975), jet fuel (ASTM D1655), or as biodiesel (ASTM D6751).
After extraction, lipid and/or hydrocarbon components recovered from the microbial biomass described herein can be subjected to chemical treatment to manufacture a fuel for use in diesel vehicles and jet engines.
Biodiesel
Biodiesel is a liquid which varies in color—between golden and dark brown—depending on the production feedstock. It is practically immiscible with water, has a high boiling point and low vapor pressure. Biodiesel refers to a diesel-equivalent processed fuel for use in diesel-engine vehicles. Biodiesel is biodegradable and non-toxic. An additional benefit of biodiesel over conventional diesel fuel is lower engine wear.
Typically, biodiesel comprises C14-C18 alkyl esters. Various processes convert biomass or a lipid produced and isolated as described herein to diesel fuels. A preferred method to produce biodiesel is by transesterification of a lipid as described herein. A preferred alkyl ester for use as biodiesel is a methyl ester or ethyl ester.
Biodiesel produced by a method described herein can be used alone or blended with conventional diesel fuel at any concentration in most modern diesel-engine vehicles. When blended with conventional diesel fuel (petroleum diesel), biodiesel may be present from about 0.1% to about 99.9%. Much of the world uses a system known as the “B” factor to state the amount of biodiesel in any fuel mix. For example, fuel containing 20% biodiesel is labeled B20. Pure biodiesel is referred to as B100.
Biodiesel can also be used as a heating fuel in domestic and commercial boilers. Existing oil boilers may contain rubber parts and may require conversion to run on biodiesel. The conversion process is usually relatively simple, involving the exchange of rubber parts for synthetic parts due to biodiesel being a strong solvent. Due to its strong solvent power, burning biodiesel will increase the efficiency of boilers.
Biodiesel can be used as an additive in formulations of diesel to increase the lubricity of pure Ultra-Low Sulfur Diesel (ULSD) fuel, which is advantageous because it has virtually no sulfur content.
Biodiesel is a better solvent than petrodiesel and can be used to break down deposits of residues in the fuel lines of vehicles that have previously been run on petrodiesel.
Production of Biodiesel
Biodiesel can be produced by transesterification of triglycerides contained in oil-rich biomass. Thus, in another aspect of the present invention a method for producing biodiesel is provided. In a preferred embodiment, the method for producing biodiesel comprises the steps of (a) cultivating a lipid-containing microorganism using methods disclosed herein (b) lysing a lipid-containing microorganism to produce a lysate, (c) isolating lipid from the lysed microorganism, and (d) transesterifying the lipid composition, whereby biodiesel is produced.
Methods for growth of a microorganism, lysing a microorganism to produce a lysate, treating the lysate in a medium comprising an organic solvent to form a heterogeneous mixture and separating the treated lysate into a lipid composition have been described above and can also be used in the method of producing biodiesel.
Lipid compositions can be subjected to transesterification to yield long-chain fatty acid esters useful as biodiesel. Preferred transesterification reactions are outlined below and include base catalyzed transesterification and transesterification using recombinant lipases.
In a base-catalyzed transesterification process, the triacylglycerides are reacted with an alcohol, such as methanol or ethanol, in the presence of an alkaline catalyst, typically potassium hydroxide. This reaction forms methyl or ethyl esters and glycerin (glycerol) as a byproduct.
General Chemical Process
Animal and plant oils are typically made of triglycerides which are esters of free fatty acids with the trihydric alcohol, glycerol. In transesterification, the glycerol in a triacylglyceride (TAG) is replaced with a short-chain alcohol such as methanol or ethanol.
Using Recombinant Lipases
Transesterification has also been carried out experimentally using an enzyme, such as a lipase instead of a base. Lipase-catalyzed transesterification can be carried out, for example, at a temperature between the room temperature and 80 C, and a mole ratio of the TAG to the lower alcohol of greater than 1:1, preferably about 3:1.
Lipases suitable for use in transesterification are found in, e.g. U.S. Pat. Nos. 4,798,793; 4,940,845 5,156,963; 5,342,768; 5,776,741 and WO89/01032.
One challenge to using a lipase for the production of fatty acid esters suitable for biodiesel is that the price of lipase is much higher than the price of sodium hydroxide (NaOH) used by the strong base process. This challenge has been addressed by using an immobilized lipase, which can be recycled. However, the activity of the immobilized lipase must be maintained after being recycled for a minimum number of cycles to allow a lipase-based process to compete with the strong base process in terms of the production cost. Immobilized lipases are subject to poisoning by the lower alcohols typically used in transesterification. U.S. Pat. No. 6,398,707 (issued Jun. 4, 2002 to Wu et al.) describes methods for enhancing the activity of immobilized lipases and regenerating immobilized lipases having reduced activity.
In particular embodiments, a recombinant lipase is expressed in the same microorganisms that produce the lipid on which the lipase acts. DNA encoding the lipase and selectable marker is preferably codon-optimized cDNA. Methods of recoding genes for expression in microalgae are described in U.S. Pat. No. 7,135,290.
Standards
The common international standard for biodiesel is EN 14214. ASTM D6751 is the most common biodiesel standard referenced in the United States and Canada. Germany uses DIN EN 14214 and the UK requires compliance with BS EN 14214.
Basic industrial tests to determine whether the products conform to these standards typically include gas chromatography, HPLC, and others. Biodiesel meeting the quality standards is very non-toxic, with a toxicity rating (LD50) of greater than 50 mL/kg.
Renewable Diesel
Renewable diesel comprises alkanes, such as C16:0 and C18:0 and thus, are distinguishable from biodiesel. High quality renewable diesel conforms to the ASTM D975 standard.
The lipids produced by the methods of the present invention can serve as feedstock to produce renewable diesel. Thus, in another aspect of the present invention, a method for producing renewable diesel is provided. Renewable diesel can be produced by at least three processes: hydrothermal processing (hydrotreating); hydroprocessing; and indirect liquefaction. These processes yield non-ester distillates. During these processes, triacylglycerides produced and isolated as described herein, are converted to alkanes.
In a preferred embodiment, the method for producing renewable diesel comprises (a) cultivating a lipid-containing microorganism using methods disclosed herein (b) lysing the microorganism to produce a lysate, (c) isolating lipid from the lysed microorganism, and (d) deoxygenating and hydrotreating the lipid to produce an alkane, whereby renewable diesel is produced. Lipids suitable for manufacturing renewable diesel can be obtained via extraction from microbial biomass using an organic solvent such as hexane, or via other methods, such as those described in U.S. Pat. No. 5,928,696.
In some methods, the microbial lipid is first cracked in conjunction with hydrotreating to reduce carbon chain length and saturate double bonds, respectively. The material is then isomerized, also in conjunction with hydrotreating. The naptha fraction can then be removed through distillation, followed by additional distillation to vaporize and distill components desired in the diesel fuel to meet a D975 standard while leaving components that are heavier than desired for meeting a D 975 standard. Hydrotreating, hydrocracking, deoxygenation and isomerization methods of chemically modifying oils, including triglyceride oils, are well known in the art. See for example European patent applications EP1741768 (A1); EP1741767 (A1); EP1682466 (A1); EP1640437 (A1); EP1681337 (A1); EP1795576 (A1); and U.S. Pat. Nos. 7,238,277; 6,630,066; 6,596,155; 6,977,322; 7,041,866; 6,217,746; 5,885,440; 6,881,873.
Hydrotreating
In a preferred embodiment of the method for producing renewable diesel, treating the lipid to produce an alkane is performed by hydrotreating of the lipid composition. In hydrothermal processing, typically, biomass is reacted in water at an elevated temperature and pressure to form oils and residual solids. Conversion temperatures are typically 300 to 660 F, with pressure sufficient to keep the water primarily as a liquid, 100 to 170 standard atmosphere (atm). Reaction times are on the order of 15 to 30 minutes. After the reaction is completed, the organics are separated from the water. Thereby a distillate suitable for diesel is produced.
Hydroprocessing
A renewable diesel, referred to as “green diesel,” can be produced from fatty acids by traditional hydroprocessing technology. The triglyceride-containing oils can be hydroprocessed either as co-feed with petroleum or as a dedicated feed. The product is a diesel fuel that conforms to the ASTM D975 specification. Thus, in another preferred embodiment of the method for producing renewable diesel, treating the lipid composition to produce an alkane is performed by hydroprocessing of the lipid composition.
In some methods of making renewable diesel, the first step of treating a triglyceride is hydroprocessing to saturate double bonds, followed by deoxygenation at elevated temperature in the presence of hydrogen and a catalyst. In some methods, hydrogenation and deoxygenation occur in the same reaction. In other methods deoxygenation occurs before hydrogenation. Isomerization is then optionally performed, also in the presence of hydrogen and a catalyst. Naphtha components are preferably removed through distillation. For examples, see U.S. Pat. No. 5,475,160 (hydrogenation of triglycerides); U.S. Pat. No. 5,091,116 (deoxygenation, hydrogenation and gas removal); U.S. Pat. No. 6,391,815 (hydrogenation); and U.S. Pat. No. 5,888,947 (isomerization).
Petroleum refiners use hydroprocessing to remove impurities by treating feeds with hydrogen. Hydroprocessing conversion temperatures are typically 300 to 700 F. Pressures are typically 40 to 100 atm. The reaction times are typically on the order of 10 to 60 minutes.
Solid catalysts are employed to increase certain reaction rates, improve selectivity for certain products, and optimize hydrogen consumption.
Hydrotreating and hydroprocessing ultimately lead to a reduction in the molecular weight of the feed. In the case of triglyceride-containing oils, the triglyceride molecule is reduced to four hydrocarbon molecules under hydroprocessing conditions: a propane molecule and three heavier hydrocarbon molecules, typically in the C8 to C18 range.
Indirect Liquefaction
A traditional ultra-low sulfur diesel can be produced from any form of biomass by a two-step process. First, the biomass is converted to a syngas, a gaseous mixture rich in hydrogen and carbon monoxide. Then, the syngas is catalytically converted to liquids. Typically, the production of liquids is accomplished using Fischer-Tropsch (FT) synthesis. This technology applies to coal, natural gas, and heavy oils. Thus, in yet another preferred embodiment of the method for producing renewable diesel, treating the lipid composition to produce an alkane is performed by indirect liquefaction of the lipid composition.
Jet Fuel
Aeroplane fuel is clear to straw colored. The most common fuel is an unleaded/paraffin oil-based fuel classified as Aeroplane A-1, which is produced to an internationally standardized set of specifications. Aeroplane fuel is a mixture of a large number of different hydrocarbons, possibly as many as a thousand or more. The range of their sizes (molecular weights or carbon numbers) is restricted by the requirements for the product, for example, freezing point or smoke point. Kerosone-type Aeroplane fuel (including Jet A and Jet A-1) has a carbon number distribution between about 8 and 16 carbon numbers. Wide-cut or naphta-type Aeroplane fuel (including Jet B) typically has a carbon number distribution between about 5 and 15 carbons.
Both Aeroplanes (Jet A and jet B) may contain a number of additives. Useful additives include, but are not limited to, antioxidants, antistatic agents, corrosion inhibitors, and fuel system icing inhibitor (FSII) agents. Antioxidants prevent gumming and usually, are based on alkylated phenols, for example, AO-30, AO-31, or AO-37. Antistatic agents dissipate static electricity and prevent sparking. Stadis 450 with dinonylnaphthylsulfonic acid (DINNSA) as the active ingredient is an example. Corrosion inhibitors, e.g., DCI-4A are used for civilian and military fuels and DCI-6A is used for military fuels. FSII agents, include, e.g., Di-EGME.
A solution is blending algae fuels with existing jet fuel. The present invention provides such a solution. The lipids produced by the methods of the present invention can serve as feedstock to produce jet fuel. Thus, in another aspect of the present invention, a method for producing jet fuel is provided. Herewith two methods for producing jet fuel from the lipids produced by the methods of the present invention are provided: fluid catalytic cracking (FCC); and hydrodeoxygenation (HDO).
Fluid Catalytic Cracking
Fluid Catalytic Cracking (FCC) is one method which is used to produce olefins, especially propylene from heavy crude fractions. There are reports in the literature that vegetable oils such as canola oil could be processed using FCC to give a hydrocarbon stream useful as a gasoline fuel.
The lipids produced by the method of the present invention can be converted to olefins. The process involves flowing the lipids produced through an FCC zone and collecting a product stream comprised of olefins, which is useful as a jet fuel. The lipids produced are contacted with a cracking catalyst at cracking conditions to provide a product stream comprising olefins and hydrocarbons useful as jet fuel.
In a preferred embodiment, the method for producing jet fuel comprises (a) cultivating a lipid-containing microorganism using methods disclosed herein, (b) lysing the lipid-containing microorganism to produce a lysate, (c) isolating lipid from the lysate, and (d) treating the lipid composition, whereby jet fuel is produced.
In a preferred embodiment of the method for producing a jet fuel, the lipid composition can be flowed through a fluid catalytic cracking zone, which, in one embodiment, may comprise contacting the lipid composition with a cracking catalyst at cracking conditions to provide a product stream comprising C2-C5 olefins.
In certain embodiments of this method it may be desirable to remove any contaminants that may be present in the lipid composition. Thus, prior to flowing the lipid composition through a fluid catalytic cracking zone, the lipid composition is pretreated. Pretreatment may involve contacting the lipid composition with an ion-exchange resin. The ion exchange resin is an acidic ion exchange resin, such as Amberlyst™-15 and can be used as a bed in a reactor through which the lipid composition is flowed, either upflow or downflow. Other pretreatments may include mild acid washes by contacting the lipid composition with an acid, such as sulfuric, acetic, nitric, or hydrochloric acid. Contacting is done with a dilute acid solution usually at ambient temperature and atmospheric pressure.
The lipid composition, optionally pretreated, is flowed to an FCC zone where the hydrocarbonaceous components are cracked to olefins. Catalytic cracking is accomplished by contacting the lipid composition in a reaction zone with a catalyst composed of finely divided particulate material. The reaction is catalytic cracking, as opposed to hydrocracking, and is carried out in the absence of added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds, substantial amounts of coke are deposited on the catalyst. The catalyst is regenerated at high temperatures by burning coke from the catalyst in a regeneration zone. Coke-containing catalyst, referred to herein as “coked catalyst”, is continually transported from the reaction zone to the regeneration zone to be regenerated and replaced by essentially coke-free regenerated catalyst from the regeneration zone. Fluidization of the catalyst particles by various gaseous streams allows the transport of catalyst between the reaction zone and regeneration zone. Methods for cracking hydrocarbons, such as those of the lipid composition described herein, in a fluidized stream of catalyst, transporting catalyst between reaction and regeneration zones, and combusting coke in the regenerator are well known by those skilled in the art of FCC processes. Exemplary FCC applications and catalysts useful for cracking the lipid composition to produce C2-C5 olefins are described in U.S. Pat. Nos. 6,538,169, 7,288,685, which are incorporated in their entirety by reference.
In one embodiment, cracking the lipid composition of the present invention, takes place in the riser section or, alternatively, the lift section, of the FCC zone. The lipid composition is introduced into the riser by a nozzle resulting in the rapid vaporization of the lipid composition. Before contacting the catalyst, the lipid composition will ordinarily have a temperature of about 149 C to about 316 C (300 F to 600 F). The catalyst is flowed from a blending vessel to the riser where it contacts the lipid composition for a time of abort 2 seconds or less.
The blended catalyst and reacted lipid composition vapors are then discharged from the top of the riser through an outlet and separated into a cracked product vapor stream including olefins and a collection of catalyst particles covered with substantial quantities of coke and generally referred to as “coked catalyst.” In an effort to minimize the contact time of the lipid composition and the catalyst which may promote further conversion of desired products to undesirable other products, any arrangement of separators such as a swirl arm arrangement can be used to remove coked catalyst from the product stream quickly. The separator, e.g. swirl arm separator, is located in an upper portion of a chamber with a stripping zone situated in the lower portion of the chamber. Catalyst separated by the swirl arm arrangement drops down into the stripping zone. The cracked product vapor stream comprising cracked hydrocarbons including light olefins and some catalyst exit the chamber via a conduit which is in communication with cyclones. The cyclones remove remaining catalyst particles from the product vapor stream to reduce particle concentrations to very low levels. The product vapor stream then exits the top of the separating vessel. Catalyst separated by the cyclones is returned to the separating vessel and then to the stripping zone. The stripping zone removes adsorbed hydrocarbons from the surface of the catalyst by counter-current contact with steam.
Low hydrocarbon partial pressure operates to favor the production of light olefins. Accordingly, the riser pressure is set at about 172 to 241 kPa (25 to 35 psia) with a hydrocarbon partial pressure of about 35 to 172 kPa (5 to 25 psia), with a preferred hydrocarbon partial pressure of about 69 to 138 kPa (10 to 20 psia). This relatively low partial pressure for hydrocarbon is achieved by using steam as a diluent to the extent that the diluent is 10 to 55 wt-% of lipid composition and preferably about 15 wt-% of lipid composition. Other diluents such as dry gas can be used to reach equivalent hydrocarbon partial pressures.
The temperature of the cracked stream at the riser outlet will be about 510 C to 621 C (950 F to 1150 F). However, riser outlet temperatures above 566 C (1050 F) make more dry gas and more olefins. Whereas, riser outlet temperatures below 566 C (1050 F) make less ethylene and propylene. Accordingly, it is preferred to run the FCC process at a preferred temperature of about 566 C to about 630 C, preferred pressure of about 138 kPa to about 240 kPa (20 to 35 psia). Another condition for the process is the catalyst to lipid composition ratio which can vary from about 5 to about 20 and preferably from about 10 to about 15.
In one embodiment of the method for producing a jet fuel, the lipid composition is introduced into the lift section of an FCC reactor. The temperature in the lift section will be very hot and range from about 700 C (1292 F) to about 760 C (1400 F) with a catalyst to lipid composition ratio of about 100 to about 150. It is anticipated that introducing the lipid composition into the lift section will produce considerable amounts of propylene and ethylene.
Gas and liquid hydrocarbon products produced can be analyzed by gas chromatography, HPLC, etc.
Hydrodeoxygenation
In another embodiment of the method for producing a jet fuel using the lipid composition or the lipids produced as described herein, the structure of the lipid composition or the lipids is broken by a process referred to as hydrodeoxygenation (HDO).
HDO means removal of oxygen by means of hydrogen, that is, oxygen is removed while breaking the structure of the material. Olefinic double bonds are hydrogenated and any sulphur and nitrogen compounds are removed. Sulphur removal is called hydrodesulphurization (HDS). Pretreatment and purity of the raw materials (lipid composition or the lipids) contribute to the service life of the catalyst.
Generally in the HDO/HDS step, hydrogen is mixed with the feed stock (lipid composition or the lipids) and then the mixture is passed through a catalyst bed as a co-current flow, either as a single phase or a two phase feed stock. After the HDO/MDS step, the product fraction is separated and passed to a separate isomerization reactor. An isomerization reactor for biological starting material is described in the literature (FI 100 248) as a co-current reactor.
The process for producing a fuel by hydrogenating a hydrocarbon feed, e.g., the lipid composition or the lipids herein, can also be performed by passing the lipid composition or the lipids as a co-current flow with hydrogen gas through a first hydrogenation zone, and thereafter the hydrocarbon effluent is further hydrogenated in a second hydrogenation zone by passing hydrogen gas to the second hydrogenation zone as a counter-current flow relative to the hydrocarbon effluent. Exemplary HDO applications and catalysts useful for cracking the lipid composition to produce C2-C5 olefins are described in U.S. Pat. No. 7,232,935, which is incorporated in its entirety by reference.
Typically, in the hydrodeoxygenation step, the structure of the biological component, such as the lipid composition or lipids herein, is decomposed, oxygen, nitrogen, phosphorus and sulphur compounds, and light hydrocarbons as gas are removed, and the olefinic bonds are hydrogenated. In the second step of the process, i.e. in the so-called isomerization step, isomerization is carried out for branching the hydrocarbon chain and improving the performance of the paraffin at low temperatures.
In the first step i.e. HDO step of the cracking process, hydrogen gas and the lipid composition or lipids herein which are to be hydrogenated are passed to a HDO catalyst bed system either as co-current or counter-current flows, said catalyst bed system comprising one or more catalyst bed(s), preferably 1-3 catalyst beds. The HDO step is typically operated in a co-current manner. In case of a HDO catalyst bed system comprising two or more catalyst beds, one or more of the beds may be operated using the counter-current flow principle.
In the HDO step, the pressure varies between 20 and 150 bar, preferably between 50 and 100 bar, and the temperature varies between 200 and 500 C, preferably in the range of 300-400 C.
In the HDO step, known hydrogenation catalysts containing metals from Group VII and/or VIB of the Periodic System may be used. Preferably, the hydrogenation catalysts are supported Pd, Pt, Ni, NiMo or a CoMo catalysts, the support being alumina and/or silica. Typically, NiMo/Al2O3 and CoMo/Al2O3 catalysts are used.
Prior to the HDO step, the lipid composition or lipids herein may optionally be treated by prehydrogenation under milder conditions thus avoiding side reactions of the double bonds. Such prehydrogenation is carried out in the presence of a prehydrogenation catalyst at temperatures of 50 400 C and at hydrogen pressures of 1 200 bar, preferably at a temperature between 150 and 250 C and at a hydrogen pressure between 10 and 100 bar. The catalyst may contain metals from Group VIII and/or VIB of the Periodic System. Preferably, the prehydrogenation catalyst is a supported Pd, Pt, Ni, NiMo or a CoMo catalyst, the support being alumina and/or silica.
A gaseous stream from the HDO step containing hydrogen is cooled and then carbon monoxide, carbon dioxide, nitrogen, phosphorus and sulphur compounds, gaseous light hydrocarbons and other impurities are removed therefrom. After compressing, the purified hydrogen or recycled hydrogen is returned back to the first catalyst bed and/or between the catalyst beds to make up for the withdrawn gas stream. Water is removed from the condensed liquid. The liquid is passed to the first catalyst bed or between the catalyst beds.
After the HDO step, the product is subjected to an isomerization step. It is substantial for the process that the impurities are removed as completely as possible before the hydrocarbons are contacted with the isomerization catalyst. The isomerization step comprises an optional stripping step, wherein the reaction product from the HDO step may be purified by stripping with water vapour or a suitable gas such as light hydrocarbon, nitrogen or hydrogen. The optional stripping step is carried out in counter-current manner in a unit upstream of the isomerization catalyst, wherein the gas and liquid are contacted with each other, or before the actual isomerization reactor in a separate stripping unit utilizing counter-current principle.
After the stripping step the hydrogen gas and the hydrogenated lipid composition or lipids herein, and optionally an n-paraffin mixture, are passed to a reactive isomerization unit comprising one or several catalyst bed(s). The catalyst beds of the isomerization step may operate either in co-current or counter-current manner.
It is important for the process that the counter-current flow principle is applied in the isomerization step. In the isomerization step this is done by carrying out either the optional stripping step or the isomerization reaction step or both in counter-current manner.
The isomerization step and the HDO step may be carried out in the same pressure vessel or in separate pressure vessels. Optional prehydrogenation may be carried out in a separate pressure vessel or in the same pressure vessel as the HDO and isomerization steps.
In the isomerization step, the pressure varies in the range of 20 150 bar, preferably in the range of 20 100 bar, the temperature being between 200 and 500 C, preferably between 300 and 400 C.
In the isomerization step, isomerization catalysts known in the art may be used. Suitable isomerization catalysts contain molecular sieve and/or a metal from Group VII and/or a carrier. Preferably, the isomerization catalyst contains SAPO-11 or SAPO41 or ZSM-22 or ZSM-23 or ferrierite and Pt, Pd or Ni and Al2O3 or SiO2. Typical isomerization catalysts are, for example, Pt/SAPO-11/Al2O3, Pt/ZSM-22/Al2O3, Pt/ZSM-23/Al2O3 and Pt/SAPO-11/SiO2.
As the product, a high quality hydrocarbon component of biological origin,useful as a diesel fuel or a component thereof, is obtained, the density, cetane number and performance at low temperate of said hydrocarbon component being excellent.
Microbe Engineering
As noted above, in certain embodiments of the present invention it is desirable to genetically modify a microorganism to enhance lipid production, modify the properties or proportions of components generated by the microorganism, or to improve or provide de novo growth characteristics on a variety of feedstock materials.
Promoters, cDNAs, and 3′UTRs, as well as other elements of the vectors, can be generated through cloning techniques using fragments isolated from native sources (see for example Molecular Cloning: A Laboratory Manual, Sambrook et al. (3d edition, 2001, Cold Spring Harbor Press; and U.S. Pat. No. 4,683,202). Alternatively, elements can be generated synthetically using known methods (see for example Gene. 1995 Oct. 16; 164(1):49-53). Microbial engineering methods are generally known in the art, e.g., U.S. Pat. App. No. 20090011480, herein incorporated by reference in its entirety, for all purposes.
EXAMPLESBelow are examples of specific embodiments for carrying out the present invention. The examples are offered for illustrative purposes only, and are not intended to limit the scope of the present invention in any way. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperatures, etc.), but some experimental error and deviation should, of course, be allowed for.
The practice of the present invention will employ, unless otherwise indicated, conventional methods of protein chemistry, biochemistry, recombinant DNA techniques and pharmacology, within the skill of the art. Such techniques are explained fully in the literature. See, e.g., T. E. Creighton, Proteins: Structures and Molecular Properties (W.H. Freeman and Company, 1993); A. L. Lehninger, Biochemistry (Worth Publishers, Inc., current addition); Sambrook, et al., Molecular Cloning: A Laboratory Manual (2nd Edition, 1989); Methods In Enzymology (S. Colowick and N. Kaplan eds., Academic Press, Inc.); Remington's Pharmaceutical Sciences, 18th Edition (Easton, Pa.: Mack Publishing Company, 1990); Carey and Sundberg Advanced Organic Chemistry 3rd Ed. (Plenum Press) Vols A and B (1992).
Example 1 Biomass Increase by Low Intensity-Illumination Application to Microalgae FermentationBotryococcus naturally synthesizes and tolerates hydrocarbon mixtures and produces as much as 85% hydrocarbon by weight, and in many cases the major hydrocarbon is botryococcenes. It is also known to be an obligate phototroph, but it seems to have the ability to uptake glucose (Reference: “Biosynthesis of the triterpenoids, botryococcenes and tetramethylsqualene in the B race of Botryococcus braunii via the non-mevalonate pathway” Sato et al. 2003. Tetrahedron Letter 44:7035-7037).
Botryococcus culture is grown on BG11 media (Reference: “Autotrophic cultivation of Botryococcus braunii for the production of hydrocarbons and exopolysaccharides in various media”. Dayananda et al. 2007. Biomass and Bioenergy. 31: 87-93) at 25-35° C. in a bioreactor with 10-30% of dissolved oxygen. The effects of light signal on heterotrophic growth of Botryococcus are tested by comparing the cellular dry weight of the cultures from different conditions (dark+no glucose, dark+glucose, light+no glucose, and light+glucose). Optimum light intensity (0.01-300 μmol photons m−2 s−1) and different light spectrum (360-700 nm) as well as different light periods (9-16 hr) are tested. Combination of low irradiance of light and glucose results in a) improved growth rate, b) increased products such as carotenoids, lipids, and botryococcenes.
Example 2 Light Regulation of Isoprenoid PathwayIsoprene, monoterpenes and sesquiterpenes are synthesized and emitted by some plant and microalgal species, but not all species have this ability. These volatile, nonessential isoprenoid compounds share the same biochemical precursors as larger commercially useful isoprenoids such as carotenoids and hydrocarbons. Two separate pathways operate in plant cells to synthesize prenyl diphosphate precursors common to all isoprenoids.
Cytosolic and mitochondrial precursors are produced by the mevalonic acid (MVA) pathway whereas the recently discovered methylerythritol phosphate (MEP) pathway is located in plastids. Botryococcus braunii produces hydrocarbon by the non-mevalonic, MEP pathway (
Light is the most important environmental factor for regulation of MEP pathway. 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) is the rate limiting step, and the expression of the gene encoding DXR is regulated by light (Reference: “Expression and molecular analysis of the Arabidopsis DXR gene encoding 1-deoxy-d-xylulose 5-phosphate reductoisomerase, the first committed enzyme of the 2-c-methyl-d-erythritol 4-phosphate pathway”. Carretero-Paulet et al. Plant Physiology. 2002. 129:1581-1591).
Another example is blue-light activation of genes encoding carotenoid biosynthetic enzymes in Chlamydomonas reinhardtii, an unicellular green alga. Microarray and quantitative PCR experiments showed the genes encoding carotenoid biosynthetic enzymes such as PDS, HDS, PSY, and ZDS are activated by very low irradiance of white light (0.01 μmol photons m−2 s−1) and blue light. Further evidence suggested phototropin, a blue light receptor, is involved in blue-light activated gene expression for carotenoid biosynthesis (Reference: “Phototropin involvement in the expression of genes encoding chlorophyll and carotenoid biosynthesis enzymes and LHC apoproteins in Chlamydomonas reinhardtii”. Im et al. The Plant Journal. 2006. 48:1-16).
One example is the increase of hydrocarbon production from Botryococcus. Various light intensity (0.01-300 μmol photons m−2 s−1) and different light spectrum (360-700 nm) are applied to a Botryococcus culture, and the amount of different hydrocarbon species are measured by GC-MS.
Example 3 Growth of Neochloris oleabundans Under Different Light Conditions
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- Materials and Methods
Microalgae and Culture Condition
Neochloris oleabundans strain UTEX 1185 was obtained from the culture collection of algae at the University of Texas (Austin, Tex. USA). Initial culture of the microalgae was grown in Erlenmeyer 250 ml flask containing 120 ml modified bold 3 N medium with 2% glucose at 25° C. room temperature with an aluminum foil loosely covering the flask on an orbital shaker at 130 rpm under alternating two 40 W natural sunshine (392316, Philips) and two 40 W plant and aquarium (392282, Philips) fluorescent light bulbs. The culture medium (modified MB3N) contained the following components per 1 L of deionized water: 0.75 g NaNO3, 0.075 g K2HPO4, 0.074 g MgSO47H2O, 0.025 g CaCl22H2O, 0.176 g KH2PO4, 0.025 g NaCl, 6 ml of P-IV metal solution (0.75 g Na2EDTA2H2O, 0.097 g FeCl36H2O, 0.041 g MnCl24H2O, 0.005 g ZnCl2, 0.002 g CoCl26H2O, 0.004 g Na2MoO4 2H2O in 1 L dI water), 1 ml of each three vitamins (0.1 mM vitamin B12, 0.1 mM biotin, 6.5 mM thiamine dissolved separately in 50 mM HEPES pH 7.8). Final pH of the medium was adjusted to 7.5 with 20% KOH before autoclaving the medium. The vitamin solutions were added to cool down the autoclaved medium. Once the initial culture reached certain confluence, its concentration was measured using optical density (OD) at 680 nm and 750 nm using Genesys 10 UV spectrophotometer (Thermo Scientific).
Experimental Procedure and Growth Measurement
Three different wavelengths of light (white, blue, and red) were tested. LED lights were purchased from Super Bright LEDs, Inc. (white: RL5-W3030, blue: RL5-B2430, red: RL5-R1330). For each light wavelength, four different conditions were set up in duplicate as follows:
1-2. Modified MB3N+no glucose+dark
3-4. Modified MB3N+no glucose+dim light
5-6. Modified MB3N+2% glucose+dark
7-8. Modified MB3N+2% glucose+dim light
A total of eight 250 ml Erlenmeyer flasks containing a final volume of 120 ml cell culture were prepared with an initial cell concentration of OD 0.1 at 750 nm (˜1.1×106 cells/ml) for each condition. Intensity of light was set at 3-4 μmol/m2s−1 photons for white, 2-3 μmol/m2s−1 photons for blue, and 1-2 μmol/m2s−1 photons for red. The speed of the orbital shaker was set at 135 rpm. The experiment was carried out at room temperature for two weeks. 1 ml of cell culture was obtained from each flask every 24 hrs to evaluate cell concentrations by measuring OD at 680 nm and 750 nm using Genesys 10 UV spectrophotometer from Thermo Fisher Scientific (Waltham, Mass. USA). Specific growth rate was determined by plotting the logarithm of culture optical density against time (
Materials and Methods
Strains and Media
Botryococcus sudeticus strain UTEX 2629 was obtained from the algae culture collection at the University of Texas (Austin, Tex. USA). Stock culture was grown in Erlenmeyer 250 ml flasks containing 120 ml modified BG11 medium with 2% glucose at 25° C. room temperature with dim light (4-5 μmol/m2s−1 photons) on an orbital shaker at 130 rpm. Dim lighting is composed of two different bulbs, 40 W natural sunshine (392316 Philips) and 40 W plant and aquarium fluorescent light bulbs (392282 Philips). 1 L of culture medium (Modified BG-11) contained: 10 mM HEPES (pH 7.8), 1.5 g NaNO3, 0.04 g K2HPO4, 0.06 g MgSO47H2O, 0.036 g CaCl22H2O, 0.006 g Citric acid H2O, 0.0138 g Ammonium Ferric Citrate, 0.001 g Na2EDTA2H2O, 0.02 g Na2CO3, 2.86 mg H3BO3, 1.81 mg MnCl24H2O, 0.22 mg ZnSO47H2O, 0.39 mg Na2MoO42H2O, 0.079 mg CuSO45H2O, 0.0494 mg Co(NO3)26H2O, 0.5 g casein hydrolysate, and 1 ml of each three vitamins (0.1 mM vitamin B12, 0.1 mM biotin, 6.5 mM thiamine dissolved separately in 50 mM HEPES pH 7.8). Final pH of the medium was adjusted to 7.8 with 20% KOH.
Experimental Procedure and Growth Measurement
Three different wavelengths of light (white, blue, and red) were tested. LED lights were purchased from Super Bright LEDs, Inc. (white: RL5-W3030, blue: RL5-B2430, red: RL5-R1330). For each light wavelength, four different conditions were set up in duplicate as follows:
1-2. Modified BG-11+no glucose+dark
3-4. Modified BG-11+no glucose+dim light
5-6. Modified BG-11+2% glucose+dark
7-8. Modified BG-11+2% glucose+dim light
A total of eight 250 ml Erlenmeyer flasks containing a final volume of 120 ml cell culture were prepared with an initial cell concentration of OD 0.1 at 750 nm (˜1.1×106 cells/ml) for each condition. Intensity of light was set at 3-4 μmol/m2s−1 photons for white, 2-3 μmol/m2s−1 photons for blue, and 1-2 μmol/m2s−1 photons for red. The speed of the orbital shaker was set at 135 rpm. The experiment was carried out at room temperature for two weeks. 1 ml of cell cultures was obtained from each flask everyday to evaluate cell concentrations by measuring OD at 680 nm and 750 nm using Genesys 10 UV spectrophotometer from Thermo Fisher Scientific (Waltham, Mass. USA). Specific growth rate was determined by plotting the logarithm of culture optical density against time (
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- Materials and Methods
Strains and Media
Botryococcus braunii strain UTEX 2441 was obtained from the algae culture collection at the University of Texas (Austin, Tex. USA). Stock culture was grown in Erlenmeyer 250 ml flasks containing 120 ml modified BG11 medium with 2% glucose at 25° C. room temperature with dim light (4-5 μmol/m2s−1 photons) on an orbital shaker at 130 rpm. Dim lighting was composed of two different bulbs, 40 W natural sunshine (392316 Philips) and 40 W plant and aquarium fluorescent light bulbs (392282 Philips). 1 L of culture medium (Modified BG-11) contained: 10 mM HEPES (pH 7.8), 1.5 g NaNO3, 0.04 g K2HPO4, 0.06 g MgSO47H2O, 0.036 g CaCl22H2O, 0.006 g Citric acid H2O, 0.0138 g Ammonium Ferric Citrate, 0.001 g Na2EDTA2H2O, 0.02 g Na2CO3, 2.86 mg H3BO3, 1.81 mg MnCl24H2O, 0.22 mg ZnSO47H2O, 0.39 mg Na2MoO42H2O, 0.079 mg CuSO45H2O, 0.0494 mg Co(NO3)26H2O, 0.5 g casein hydrolysate, and 1 ml of each three vitamins (0.1 mM vitamin B12, 0.1 mM biotin, 6.5 mM thiamine dissolved separately in 50 mM HEPES pH 7.8). Final pH of the medium was adjusted to 7.8 with 20% KOH.
Experimental Procedure and Growth Measurement
Three different wavelengths of lights (white, blue, and red) were tested. LED lights were purchased from Super Bright LEDs, Inc. (white: RL5-W3030, blue: RL5-B2430, red: RL5-R1330). For each light wavelength, four different conditions were set up in duplicate as follows:
1-2 Modified BG-11+no glucose+dark
3-4 Modified BG-11+no glucose+dim light
5-6 Modified BG-11+2% glucose+dark
7-8 Modified BG-11+2% glucose+dim light
A total of eight 250 ml Erlenmeyer flasks containing a final volume of 120 ml cell culture were prepared with an initial cell concentration of O.D 0.1 at 750 nm (˜1.1×106 cells/ml) for each condition. The intensity of light was set at 3-4 μmol/m2s−3 photons for white, 2-3 μmol/m2s−1 photons for blue, and 1-2 μmol/m2s−1 photons far red. The speed of the orbital shaker was set at 150 rpm. The experiment was carried out at room temperature for two weeks. 5 ml of each cell culture was obtained from each flask every two days to evaluate cell growth by dry cell weight (DCW). Specific growth rate was determined by plotting the culture DCW against time (
Fluorescence Measurement of Neutral Lipid by Using Nile Red
In 1 ml of algal suspension, 4 ul of Nile Red solution in acetone (250 ug/ml) was added. The mixture was vortexed 2 times during a 10 minute incubation at room temperature. After incubation, 200 ul of stained algal samples were transferred into individual wells in a 96-well plate. Fluorescence was measured on a Molecular Devices 96 well plate spectrofluorometer with a 490 nm excitation and 585 nm emission wavelength with 530 emission filter cut off. In order to determine the relative fluorescence intensity of algal samples, blank (Nile Red alone in the medium) was subtracted from the fluorescence intensity.
Results
Red light+glucose increased the growth rate of UTEX 2441 by 35% compared to heterotrophic culture in the dark (Dark+glu) (
Materials and Methods
Strains and Media
Chlamydomonas reinhardtii strain UTEX 2243 was obtained from the algae culture collection at the University of Texas (Austin, Tex. USA). Stock cultures were grown separately in Erlenmeyer 250 ml flasks containing 120 ml TAP medium at 25° C. room temperature with dim light (4-5 μmol/m2s−1 photons) on an orbital shaker at 130 rpm. Dim lighting was composed of two different bulbs (40 W natural sunshine (392316 Philips) and 40 W plant and aquarium fluorescent light bulbs (392282 Philips)). 1 L of culture medium (TAP) contained: 2.42 g Tris, 25 ml of TAP salts solution (15 g NH4Cl, 4 g MgSO47H2O, 2 g CaCl22H2O), 0.375 ml Phosphate solution (28.8 g K2HPO4, 14.4 g KH2PO4 in 100 ml of water), 1 ml Hutner's trace elements solution (1 L of Trace metal solution contains 50 g EDTA disodium Salt, 22 g ZnSO47H2O, 11.4 g H3BO4, 5.06 g MnCl24H2O, 1.61 g CoCl26H2O, 1.57 g CuSO45H2O, 1.10 (NH4)6Mo7O244H2O, 4.99 g FeSO47H2O with pH 7.0 using either KOH or HCl) and 1 ml of glacial acetic acid. Final pH of medium is 7.0 adjusted with glacier acetic acid. Tris minimal medium (TP) was made with all components listed above except acetic acid. The medium's pH was adjusted to 7.0 with HCl.
Experimental Procedure and Growth Measurement
LED lights were purchased from Super Bright LEDs, Inc. (RL5-W3030). Four different conditions were set up in duplicate as follows:
1-2. TP (no acetic acid)+dark
3-4. TP (no acetic acid)+dim light
5-6. TAP (acetic acid)+dark
7-8. TAP (acetic acid)+dim light
A total of eight 250 ml Erlenmeyer flasks containing a final volume of 120 ml cell culture were prepared with an initial cell concentration of 1.0×105 cells/ml for each condition. The intensity of light was set at 3-5 μmol/m2s−1 photons. The speed of the orbital shaker was set at 140 rpm. The experiment was carried out at room temperature for one week. 500 ul of cell culture was obtained from each flask every day to evaluate cell growth by counting cell numbers. Cells were deflagellated using lugol solution (1:20) prior to counting. Specific growth rate was determined by plotting the cell number against time. The combination of a low irradiance of white light and TAP resulted in an improved growth rate compared to controls (
Materials and Methods
Strains and Media
Microalgae strains (e.g., Chlamydomonas, Botryococcus, Neochloris, Cyanophyta, Chlorophyta, Rhodophyta, Cryptophyta, Chlorarachniophyta, Haptophyta, Euglenophyta, Heterokontophyta, Diatoms and/or those described in the description above) are obtained from, e.g. the algae culture collection at the University of Texas (Austin, Tex. USA). Stock culture is grown, e.g., in Erlenmeyer 250 ml flasks containing the appropriate medium (see, e.g., manufacturer's instructions) at about 25° C. room temperature with dim light (e.g., 4-5 μmol/m2s−1 photons) on an orbital shaker at about 130 rpm. An appropriate carbon source is used in the culture media, e.g., glucose. Dim lighting can be composed of two different bulbs, e.g., 40 W natural sunshine (392316 Philips) and 40 W plant and aquarium fluorescent light bulbs (392282 Philips). The final pH of the medium is adjusted as appropriate for the particular strain. See, e.g., manufacturer's instructions.
Experimental Procedure and Growth Measurement
Three different wavelengths of light (white, blue, and red) are tested. LED lights are purchased from, e.g., Super Bright LEDs, Inc. (white: RL5-W3030, blue: RL5-B2430, red: RL5-R1330). For each light wavelength, four different conditions are set up in duplicate as follows:
1-2 no carbon+dark
3-4 no carbon+dim light
5-6 carbon+dark
7-8 carbon+dim light
A total of eight 250 ml Erlenmeyer flasks containing a final volume of 120 ml cell culture are prepared with an initial cell concentration of, e.g., O.D 0.1 at 750 nm (˜1.1×106 cells/ml) for each condition. Optimum light intensity (e.g., 0.01-300 μmol photons m−2 s−1) and different light spectrums (e.g., 360-700 nm) as well as different light periods (e.g., 9-16 hr of light) are tested. The intensity of light is set at, e.g., 3-4 μmol/m2s−1 photons for white, 2-3 μmol/m2s−1 photons for blue, and 1-2 μmol/m2s−1 photons for red. Various carbon sources at various concentrations are tested, e.g., glucose, sucrose, fructose at a concentration of, e.g., 1%, 2%, or 3% of culture media. The speed of the orbital shaker is set at, e.g., 150 rpm. The experiment is carried out at room temperature for less than one, one, two, three, or more weeks. An aliquot of each cell culture is obtained from each flask every one to two days to evaluate cell growth by, e.g., dry cell weight (DCW). Specific growth rate is determined by plotting the culture DCW against time.
Measurement of Material of Interest
The amount of material of interest (hydrocarbon, lipid, etc.) in the media is measured using standard means known in the art, e.g., GC-MS or Nile Red as described above. For example, in 1 ml of algal suspension, 4 ul of Nile Red solution in acetone (250 ug/ml) is added. The mixture is vortexed during incubation at room temperature. After incubation, 100-200 ul of stained algal samples are transferred into individual wells in a 96-well plate. Fluorescence is measured on, e.g., a Molecular Devices 96 well plate spectrofluorometer with a 490 nm excitation and 585 nm emission wavelength with 530 emission filter cut off. In order to determine the relative fluorescence intensity of algal samples, blank (Nile Red alone in the medium) is subtracted from the fluorescence intensity.
Results
Red, white, and/or blue light in combination with a carbon source increase the growth rate of the microalgae strain compared to controls. Material of interest (e.g., hydrocarbon or lipid) levels produced by the experimental microalgae strain (red, white, and/or blue light in combination with a carbon source) increase compared to controls.
While the invention has been particularly shown and described with reference to a preferred embodiment and various alternate embodiments, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention.
All references, issued patents and patent applications cited within the body of the instant specification are hereby incorporated by reference in their entirety, for all purposes.
Claims
1. A method for cultivating a microalgae comprising a photoreceptor sensitive to a particular region of a visible spectrum under a heterotrophic growth condition, comprising:
- incubating the microalgae under the heterotrophic growth condition for a period of time sufficient to allow the microalgae to grow,
- wherein the heterotrophic growth condition comprises:
- a media comprising a carbon source, and
- an irradiance of light including the particular region of the visible spectrum in a sufficient intensity to transduce the photoreceptor.
2. The method of claim 1, wherein the microalgae is a Botryococcus strain, wherein the carbon source is glucose, and wherein the irradiance of light is between 1-10 μmol photons m−2s−1.
3. The method of claim 1, wherein the microalgae is a Botryococcus sudeticus strain, a Botryococcus strain, a UTEX 2629 strain, a Botryococcus braunii strain, a UTEX 2441 strain, a Neochloris oleabundans strain, a Neochloris strain, a UTEX 1185 strain, a Chlamydomonas reinhardtii strain, a Chlamydomonas strain, a UTEX 2243 strain, or a strain comprising a photoreceptor.
4. The method of claim 2, wherein the microalgae is a UTEX 2629 strain or a UTEX 2441 strain.
5. The method of claim 1, wherein the carbon source is glucose.
6. The method of claim 1, wherein the carbon source is selected from the group consisting of a fixed carbon source, glucose, fructose, sucrose, galactose, xylose, mannose, rhamnose, N-acetylglucosamine, glycerol, floridoside, glucuronic acid, corn starch, depolymerized cellulosic material, sugar cane, sugar beet, lactose, milk whey, and molasses.
7. The method of claim 1, wherein the light is produced by an artificial light source, or the light is artificial light.
8. The method of claim 1, wherein the intensity of the irradiance of light is between 0.01-1 μmol photons m−2s−1, between 1-10 μmol photons m−2s−1, between 10-100 μmol photons m−2s−1, between 100-300 μmol photons m−2s−1, 3-4 μmol/m2s−1 photons, 2-3 μmol/m2s−1 photons, 1-2 μmol/m2s−1 photons, or 3-5 μmol/m2s−1 photons.
9. The method of claim 1, further comprising producing a material from the microalgae.
10. The method of claim 9, wherein the material is a polysaccharide, a pigment, a lipid, or a hydrocarbon.
11. The method of claim 9, wherein the material is a hydrocarbon.
12. The method of claim 9, further comprising recovering the material.
13. The method of claim 9, further comprising extracting the material.
14. The method of claim 9, further comprising processing the material.
15. The method of claim 12, further comprising processing the material.
16. The method of claim 14, wherein the processing of the material produces a processed material.
17. The method of claim 16, wherein the processed material is selected from the group consisting of a fuel, biodiesel, jet fuel, a cosmetic, a pharmaceutical agent, a surfactant, and a renewable diesel.
18. A method of manufacturing a material, comprising:
- providing a microalgae comprising a photoreceptor sensitive to a particular region of a visible spectrum and capable of producing the material;
- culturing the microalgae in a media, wherein the media comprises a carbon source;
- applying an irradiance of light including the particular region of the visible spectrum in a sufficient intensity to transduce the photoreceptor; and
- allowing the microalgae to accumulate at least 10% of its dry cell weight as the material.
19. A bioreactor system, comprising:
- a bioreactor;
- a culture medium comprising a carbon source, wherein the culture medium is located inside the bioreactor;
- a microalgae comprising a photoreceptor sensitive to a particular region of a visible spectrum and adapted for heterotrophic growth, wherein the microalgae is located in the culture media; and
- a light source, wherein the light source produces an irradiance of light including the particular region of the visible spectrum in a sufficient intensity to transduce the photoreceptor,
- and wherein the light source is operatively coupled to the bioreactor.
Type: Application
Filed: Dec 29, 2017
Publication Date: May 24, 2018
Inventors: Chung-Soon Im (Palo Alto, CA), Jane Kim (San Jose, CA)
Application Number: 15/859,219
