PRODUCTION OF FATTY ACIDS & DERIVATIVES THEREOF
Compositions and methods for production of fatty alcohols using recombinant microorganisms are provided as well as fatty alcohol compositions produced by such methods.
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This application is a continuation of copending U.S. patent application Ser. No. 12/278,957, filed Apr. 20, 2010, as the U.S. national phase of Patent Cooperation Treaty Application No. PCT/US2007/11923, filed May 18, 2007, which claims benefit to U.S. Provisional Application Nos. 60/908,547 filed Mar. 28, 2007; U.S. Provisional Application No. 60/801,995 filed May 19, 2006, and U.S. Provisional Application No. 60/802,016 filed May 19, 2006, and, all of which are herein incorporated by reference.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ELECTRONICALLYIncorporated by reference in its entirety herein is a computer-readable nucleotide/amino acid sequence listing submitted concurrently herewith and identified as follows: One 80,354 Byte ASCII (Text) file named “PCT_SeqLstgAsFiled—05.18.07” created on May 18, 2007. It is understood that the Patent and Trademark Office will make the necessary changes in application number and filing date for the instant application.
FIELDCompositions and methods for production of fatty alcohols using recombinant microorganisms e are provided as well as fatty alcohol compositions produced by such methods.
BACKGROUNDDevelopments in technology have been accompanied by an increased reliance on fuel sources and such fuel sources are becoming increasingly limited and difficult to acquire. With the burning of fossil fuels taking place at an unprecedented rate, it has likely that the world's fuel demand will soon outweigh the current fuel supplies.
As a result, efforts have been directed toward harnessing sources of renewable energy, such as sunlight, water, wind, and biomass. The use of biomasses to produce new sources of fuel which are not derived from petroleum sources, (i.e. biofuel) has emerged as one alternative option. Biofuel (biodiesel) is a biodegradable, clean-burning combustible fuel made of long chain alkanes and esters. Biodiesel can be used in most internal combustion diesel engines in either a pure form, which is referred to as “neat” biodiesel, or as a mix in any concentration with regular petroleum diesel. Current methods of making biodiesel involve transesterification of triacylglycerides (mainly vegetable oil) which leads to a mixture of fatty acid esters and the unwanted side product glycerin, thus, providing a product that is heterogeneous and a waste product that causes economic inefficiencies.
SUMMARYDisclosed herein are recombinant microorganisms that are capable of synthesizing products derived from the fatty acid biosynthetic pathway (fatty alcohols), and optionally releasing such products into the fermentation broth. Such fatty alcohols are useful, inter alia, specialty chemicals. These specialty chemicals can be used to make additional products, such as nutritional supplements, polymers, paraffin replacements, and personal care products.
The recombinant microorganisms disclosed herein can be engineered to yield various fatty alcohol compositions.
In one example, the disclosure provides a method for modifying a microorganism so that it produces, and optionally releases, fatty alcohols generated from a renewable carbon source. Such microorganisms are genetically engineered, for example, by introducing an exogenous DNA sequence encoding one or more proteins capable of metabolizing a renewable carbon source to produce, and in some examples secrete, a fatty alcohol composition. The modified microorganisms can then be used in a fermentation process to produce useful fatty alcohols using the renewable carbon source (biomass) as a starting material. In some examples, an existing genetically tractable microorganism is used because of the ease of engineering its pathways for controlling growth, production and reducing or eliminating side reactions that reduce biosynthetic pathway efficiencies.
Provided herein are microorganisms that produce fatty alcohols having defined carbon chain length, branching, and saturation levels. In particular examples, the production of homogeneous products decreases the overall cost associated with fermentation and separation Microorganisms expressing one or more exogenous nucleic acid sequences encoding at least one thioesterase (EC 3.1.2.14) and at least one fatty alcohol forming acyl-CoA reductase (1.1.1.*) are provided. The thioesterase peptides encoded by the exogenous nucleic acid sequences can be chosen to provide homogeneous products.
In some examples the microorganism that is engineered to produce the fatty acid derivative is E. coli, Z. mobilis, Rhodococcus opacus, Ralstonia eutropha, Vibrio furnissii, Saccharomyces cerevisiae, Lactococcus lactis, Streptomycetes, Stenotrophomonas maltophila, Pseudomonas or Micrococus leuteus and their relatives.
In addition to being engineered to express exogenous nucleic acid sequences that allow for the production of fatty alcohols, the microorganism can additionally have one or more endogenous genes functionally deleted or attenuated.
In addition to being engineered to express exogenous nucleic acid sequences that allow for the production of fatty alcohols, the microorganism can additionally have one or more additional genes over-expressed.
In some examples, the microorganisms described herein produce at least 1 mg of fatty alcohol per liter fermentation broth. In other examples the microorganisms produce at least 100 mg/L, 500 mg/L, 1 g/L, 5 g/L, 10 g/L, 20 g/L, 25 g/L, 30 g/L, 35 g/L, 40 g/L, 50 g/L, 100 g/L, or 120 g/L of fatty alcohol per liter fermentation broth. In some examples, the fatty alcohol is produced and released from the microorganism and in yet other examples the microorganism is lysed prior to separation of the product.
In some examples, the fatty alcohol includes a carbon chain that is at least 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, or 34 carbons long. In some examples at least 50%, 60%, 70%, 80%, 85%, 90%, or 95% of the fatty alcohol product made contains a carbon chain that is 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, or 34 carbons long. In yet other examples, at least 60%, 70%, 80%, 85%, 90%, or 95% of the fatty alcohol product contain 1, 2, 3, 4, or 5, points of unsaturation
Also provided are methods of producing alcohol. These methods include culturing the microorganisms described herein and separating the product from the fermentation broth.
These and other examples are described further in the following detailed description.
The following explanations of terms and methods are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. As used herein, “comprising” means “including” and the singular forms “a” or “an” or “the” include plural references unless the context clearly dictates otherwise. For example, reference to “comprising a cell” includes one or a plurality of such cells, and reference to “comprising the thioesterase” includes reference to one or more thioesterase peptides and equivalents thereof known to those of ordinary skill in the art, and so forth. The term “or” refers to a single element of stated alternative elements or a combination of two or more elements, unless the context clearly indicates otherwise. For example, the phrase “thioesterase activity or fatty alcohol-forming acyl-CoA reductase activity” refers to thioesterase activity, fatty alcohol forming acyl-CoA reductase activity, or a combination of both fatty alcohol forming acyl-CoA reductase activity, and thioesterase activity.
Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Other features of the disclosure are apparent from the following detailed description and the claims.
Accession Numbers: The accession numbers throughout this description are derived from the NCBI database (National Center for Biotechnology Information) maintained by the National Institute of Health, U.S.A. The accession numbers are as provided in the database on Mar. 27, 2007.
Enzyme Classification Numbers (EC): The EC numbers provided throughout this description are derived from the KEGG Ligand database, maintained by the Kyoto Encyclopedia of Genes and Genomics, sponsored in part by the University of Tokyo. The EC numbers are as provided in the database on Mar. 27, 2007.
Attenuate: To lessen the impact, activity or strength of something. In one example, the sensitivity of a particular enzyme to feedback inhibition or inhibition caused by a composition that is not a product or a reactant (non-pathway specific feedback) is lessened such that the enzyme activity is not impacted by the presence of a compound. For example, the fabH gene and its corresponding amino acid sequence are temperature sensitive and can be altered to decrease the sensitivity to temperature fluctuations. The attenuation of the fabH gene can be used when branched amino acids are desired. In another example, an enzyme that has been altered to be less active can be referred to as attenuated.
A functional deletion of an enzyme can be used to attenuate an enzyme. A functional deletion is a mutation, partial or complete deletion, insertion, or other variation made to a gene sequence or a sequence controlling the transcription of a gene sequence, which reduces or inhibits production of the gene product, or renders the gene product non-functional (i.e. the mutation described herein for the plsB gene). For example, functional deletion of fabR in E. coli reduces the repression of the fatty acid biosynthetic pathway and allows E. coli to produce more unsaturated fatty acids (UFAs). In some instances a functional deletion is described as a knock-out mutation.
One of ordinary skill in the art will appreciate that there are many methods of attenuating enzyme activity. For example, attenuation can be accomplished by introducing amino acid sequence changes via altering the nucleic acid sequence, placing the gene under the control of a less active promoter, expressing interfering RNA, ribozymes or antisense sequences that targeting the gene of interest, or through any other technique known in the art.
Carbon source: Generally refers to a substrate or compound suitable to be used as a source of carbon for prokaryotic or simple eukaryotic cell growth. Carbon sources can be in various forms, including, but not limited to polymers, carbohydrates, acids, alcohols, aldehydes, ketones, amino acids, peptides, etc. These include, for example, various monosaccharides such as glucose, oligosaccharides, polysaccharides, cellulosic material, xylose, and arabinose, disaccharides, such sucrose, saturated or unsaturated fatty acids, succinate, lactate, acetate, ethanol, etc., or mixtures thereof. The carbon source can additionally be a product of photosynthesis, including, but not limited to glucose.
cDNA (complementary DNA): A piece of DNA lacking internal, non-coding segments (introns) and regulatory sequences which determine transcription. cDNA can be synthesized by reverse transcription from messenger RNA extracted from cells.
Deletion: The removal of one or more nucleotides from a nucleic acid molecule or one or more amino acids from a protein, the regions on either side being joined together.
Detectable: Capable of having an existence or presence ascertained. For example, production of a product from a reactant, for example, the production of C18 fatty acids, is detectable using the method provided in Example 11 below.
DNA: Deoxyribonucleic acid. DNA is a long chain polymer which includes the genetic material of most living organisms (some viruses have genes including ribonucleic acid, RNA). The repeating units in DNA polymers are four different nucleotides, each of which includes one of the four bases, adenine, guanine, cytosine and thymine bound to a deoxyribose sugar to which a phosphate group is attached. Triplets of nucleotides, referred to as codons, in DNA molecules code for amino acid in a peptide. The term codon is also used for the corresponding (and complementary) sequences of three nucleotides in the mRNA into which the DNA sequence is transcribed.
Endogenous: As used herein with reference to a nucleic acid molecule and a particular cell or microorganism refers to a nucleic acid sequence or peptide that is in the cell and was not introduced into the cell using recombinant engineering techniques. For example, a gene that was present in the cell when the cell was originally isolated from nature. A gene is still considered endogenous if the control sequences, such as a promoter or enhancer sequences that activate transcription or translation have been altered through recombinant techniques.
Exogenous: As used herein with reference to a nucleic acid molecule and a particular cell refers to any nucleic acid molecule that does not originate from that particular cell as found in nature. Thus, a non-naturally-occurring nucleic acid molecule is considered to be exogenous to a cell once introduced into the cell. A nucleic acid molecule that is naturally-occurring also can be exogenous to a particular cell. For example, an entire coding sequence isolated from cell X is an exogenous nucleic acid with respect to cell Y once that coding sequence is introduced into cell Y, even if X and Y are the same cell type.
Expression: The process by which a gene's coded information is converted into the structures and functions of a cell, such as a protein, transfer RNA, or ribosomal RNA. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (for example, transfer and ribosomal RNAs).
Fatty ester: Includes any ester made from a fatty acid. The carbon chains in fatty acids can contain any combination of the modifications described herein. For example, the carbon chain can contain one or more points of unsaturation, one or more points of branching, including cyclic branching, and can be engineered to be short or long. Any alcohol can be used to form fatty acid esters, for example alcohols derived from the fatty acid biosynthetic pathway, alcohols produced by the production host through non-fatty acid biosynthetic pathways, and alcohols that are supplied in the fermentation broth.
Fatty acid derivative: Includes products made in part from the fatty acid biosynthetic pathway of the host organism. The fatty acid biosynthetic pathway includes fatty acid synthase enzymes which can be engineered as described herein to produce fatty acid derivatives, and in some examples can be expressed with additional enzymes to produce fatty acid derivatives having desired carbon chain characteristics. Exemplary fatty acid derivatives include for example, short and long chain alcohols, hydrocarbons, and fatty acid esters including waxes.
Fermentation Broth: Includes any medium which supports microorganism life (i.e. a microorganism that is actively metabolizing carbon). A fermentation medium usually contains a carbon source. The carbon source can be anything that can be utilized, with or without additional enzymes, by the microorganism for energy.
Hydrocarbon: includes chemical compounds that containing the elements carbon (C) and hydrogen (H). All hydrocarbons consist of a carbon backbone and atoms of hydrogen attached to that backbone. Sometimes, the term is used as a shortened form of the term “aliphatic hydrocarbon.” There are essentially three types of hydrocarbons: (1) aromatic hydrocarbons, which have at least one aromatic ring; (2) saturated hydrocarbons, also known as alkanes, which lack double, triple or aromatic bonds; and (3) unsaturated hydrocarbons, which have one or more double or triple bonds between carbon atoms, are divided into: alkenes, alkynes, and dienes. Liquid geologically-extracted hydrocarbons are referred to as petroleum (literally “rock oil”) or mineral oil, while gaseous geologic hydrocarbons are referred to as natural gas. All are significant sources of fuel and raw materials as a feedstock for the production of organic chemicals and are commonly found in the Earth's subsurface using the tools of petroleum geology. Oil reserves in sedimentary rocks are the principal source of hydrocarbons for the energy and chemicals industries. Hydrocarbons are of prime economic importance because they encompass the constituents of the major fossil fuels (coal, petroleum, natural gas, etc.) and biofuels, as well as plastics, waxes, solvents and oils.
Isolated: An “isolated” biological component (such as a nucleic acid molecule, protein, or cell) has been substantially separated or purified away from other biological components in which the component naturally occurs, such as other chromosomal and extrachromosomal DNA and RNA, and proteins. Nucleic acid molecules and proteins that have been “isolated” include nucleic acid molecules and proteins purified by standard purification methods. The term also embraces nucleic acid molecules and proteins prepared by recombinant expression in a host cell as well as chemically synthesized nucleic acid molecules and proteins.
In one example, isolated refers to a naturally-occurring nucleic acid molecule that is not immediately contiguous with both of the sequences with which it is immediately contiguous (one on the 5′ end and one on the 3′ end) in the naturally-occurring genome of the organism from which it is derived.
Microorganism: Includes prokaryotic and eukaryotic microbial species from the Domains Archaea, Bacteria and Eucarya, the latter including yeast and filamentous fungi, protozoa, algae, or higher Protista. The terms “microbial cells” and “microbes” are used interchangeably with the term microorganism.
Nucleic Acid Molecule: Encompasses both RNA and DNA molecules including, without limitation, cDNA, genomic DNA, and mRNA. Includes synthetic nucleic acid molecules, such as those that are chemically synthesized or recombinantly produced. The nucleic acid molecule can be double-stranded or single-stranded. Where single-stranded, the nucleic acid molecule can be the sense strand or the antisense strand. In addition, nucleic acid molecule can be circular or linear.
Operably linked: A first nucleic acid sequence is operably linked with a second nucleic acid sequence when the first nucleic acid sequence is placed in a functional relationship with the second nucleic acid sequence. For instance, a promoter is operably linked to a coding sequence if the promoter affects the transcription or expression of the coding sequence. Generally, operably linked DNA sequences are contiguous and, where necessary to join two protein coding regions, in the same reading frame. Configurations of separate genes that are transcribed in tandem as a single messenger RNA are denoted as operons. Thus placing genes in close proximity, for example in a plasmid vector, under the transcriptional regulation of a single promoter, constitutes a synthetic operon.
ORF (open reading frame): A series of nucleotide triplets (codons) coding for amino acids without any termination codons. These sequences are usually translatable into a peptide.
Over-expressed: When a gene is caused to be transcribed at an elevated rate compared to the endogenous transcription rate for that gene. In some examples, over-expression additionally includes an elevated rate of translation of the gene compared to the endogenous translation rate for that gene. Methods of testing for over-expression are well known in the art, for example transcribed RNA levels can be assessed using rtPCR and protein levels can be assessed using SDS page gel analysis.
Purified: The term purified does not require absolute purity; rather, it is intended as a relative term. Thus, for example, a purified fatty acid derivative preparation, such as a wax, or a fatty acid ester preparation, is one in which the product is more concentrated than the product is in its environment within a cell. For example, a purified wax is one that is substantially separated from cellular components (nucleic acids, lipids, carbohydrates, and other peptides) that can accompany it. In another example, a purified wax preparation is one in which the wax is substantially-free from contaminants, such as those that might be present following fermentation.
In one example, a fatty acid ester is purified when at least about 50% by weight of a sample is composed of the fatty acid ester, for example when at least about 60%, 70%, 80%, 85%, 90%, 92%, 95%, 98%, or 99% or more of a sample is composed of the fatty acid ester. Examples of methods that can be used to purify a waxes, fatty alcohols, and fatty acid esters, include the methods described in Example 11 below.
Recombinant: A recombinant nucleic acid molecule or protein is one that has a sequence that is not naturally occurring, has a sequence that is made by an artificial combination of two otherwise separated segments of sequence, or both. This artificial combination can be achieved, for example, by chemical synthesis or by the artificial manipulation of isolated segments of nucleic acid molecules or proteins, such as genetic engineering techniques. Recombinant is also used to describe nucleic acid molecules that have been artificially manipulated, but contain the same regulatory sequences and coding regions that are found in the organism from which the nucleic acid was isolated. A recombinant cell or microorganism is one that contains an exogenous nucleic acid molecule, such as a recombinant nucleic acid molecule.
Release: The movement of a compound from inside a cell (intracellular) to outside a cell (extracellular). The movement can be active or passive. When release is active it can be facilitated by one or more transporter peptides and in some examples it can consume energy. When release is passive, it can be through diffusion through the membrane and can be facilitated by continually collecting the desired compound from the extracellular environment, thus promoting further diffusion. Release of a compound can also be accomplished by lysing a cell.
Surfactants: Substances capable of reducing the surface tension of a liquid in which they are dissolved. They are typically composed of a water-soluble head and a hydrocarbon chain or tail. The water soluble group is hydrophilic and can be either ionic or nonionic, and the hydrocarbon chain is hydrophobic. Surfactants are used in a variety of products, including detergents and cleaners, and are also used as auxiliaries for textiles, leather and paper, in chemical processes, in cosmetics and pharmaceuticals, in the food industry and in agriculture. In addition, they can be used to aid in the extraction and isolation of crude oils which are found hard to access environments or as water emulsions.
There are four types of surfactants characterized by varying uses. Anionic surfactants have detergent-like activity and are generally used for cleaning applications. Cationic surfactants contain long chain hydrocarbons and are often used to treat proteins and synthetic polymers or are components of fabric softeners and hair conditioners. Amphoteric surfactants also contain long chain hydrocarbons and are typically used in shampoos. Non-ionic surfactants are generally used in cleaning products.
Transformed or recombinant cell: A cell into which a nucleic acid molecule has been introduced, such as an acyl-CoA synthase encoding nucleic acid molecule, for example by molecular biology techniques. Transformation encompasses all techniques by which a nucleic acid molecule can be introduced into such a cell, including, but not limited to, transfection with viral vectors, conjugation, transformation with plasmid vectors, and introduction of naked DNA by electroporation, lipofection, and particle gun acceleration.
Under conditions that permit product production: Any fermentation conditions that allow a microorganism to produce a desired product, such as fatty acids, hydrocarbons, fatty alcohols, waxes, or fatty acid esters. Fermentation conditions usually include temperature ranges, levels of aeration, and media selection, which when combined allow the microorganism to grow. Exemplary mediums include broths or gels. Generally, the medium includes a carbon source such as glucose, fructose, cellulose, or the like that can be metabolized by the microorganism directly, or enzymes can be used in the medium to facilitate metabolizing the carbon source. To determine if culture conditions permit product production, the microorganism can be cultured for 24, 36, or 48 hours and a sample can be obtained and analyzed. For example, the cells in the sample or the medium in which the cells were grown can be tested for the presence of the desired product. When testing for the presence of a product assays, such as those provided in the Examples below, can be used.
Vector: A nucleic acid molecule as introduced into a cell, thereby producing a transformed cell. A vector can include nucleic acid sequences that permit it to replicate in the cell, such as an origin of replication. A vector can also include one or more selectable marker genes and other genetic elements known in the art.
Wax: A variety of fatty acid esters which form solids or pliable substances under an identified set of physical conditions. Fatty acid esters that are termed waxes generally have longer carbon chains than fatty acid esters that are not waxes. For example, a wax generally forms a pliable substance at room temperature.
DETAILED DESCRIPTION I. Production of Fatty Acid DerivativesThe host organism that exogenous DNA sequences are transformed into can be a modified host organism, such as an organism that has been modified to increase the production of acyl-ACP or acyl-CoA, reduce the catabolism of fatty acid derivatives and intermediates, or to reduce feedback inhibition at specific points in the biosynthetic pathway. In addition to modifying the genes described herein additional cellular resources can be diverted to over produce fatty acids, for example the lactate, succinate and/or acetate pathways can be attenuated, and acetyl-CoA carboxylase (ACC) can be over expressed. The modifications to the production host described herein can be through genomic alterations, extrachromosomal expression systems, or combinations thereof. An overview of the pathway is provided in
A. Acetyl-CoA--Malonyl-CoA to Acyl-ACP
Fatty acid synthase (FAS) is a group of peptides that catalyze the initiation and elongation of acyl chains (Marrakchi et al., Biochemical Society, 30:1050-1055, 2002). The acyl carrier protein (ACP) along with the enzymes in the FAS pathway control the length, degree of saturation and branching of the fatty acids produced. Enzymes that can be included in FAS include AccABCD, FabD, FabH, FabG, FabA, FabZ, FabI, FabK, FabL, FabM, FabB, and FabF. Depending upon the desired product one or more of these genes can be attenuated or over-expressed.
For example, the fatty acid biosynthetic pathway in the production host uses the precursors acetyl-CoA and malonyl-CoA (
Additionally, fadE, gpsA, ldhA, pflb, adhE, pta, poxB, ackA, and/or ackB can be knocked-out, or their expression levels can be reduced, in the engineered microorganism by transformation with conditionally replicative or non-replicative plasmids containing null or deletion mutations of the corresponding genes, or by substituting promoter or enhancer sequences. Exemplary Genbank accession numbers for these genes are; fadE (AAC73325), gspA (AAC76632), ldhA (AAC74462), pflb (AAC73989), adhE (AAC74323), pta (AAC75357), poxB (AAC73958), ackA (AAC75356), and ackB (BAB81430).
The resulting engineered microorganisms can be grown in a desired environment, for example one with limited glycerol (less than 1% w/v in the culture medium). As such, these microorganisms will have increased acetyl-CoA production levels. Malonyl-CoA overproduction can be effected by engineering the microorganism as described above, with DNA encoding accABCD (acetyl CoA carboxylase, for example accession number AAC73296, EC 6.4.1.2) included in the plasmid synthesized de novo. Fatty acid overproduction can be achieved by further including DNA encoding lipase (for example Accessions numbers CAA89087, CAA98876) in the plasmid synthesized de novo.
In some examples, acetyl-CoA carboxylase (ACC) is over-expressed to increase the intracellular concentration thereof by at least 2-fold, such as at least 5-fold, or at least 10-fold, for example relative to native expression levels.
In addition, the plsB (for example Accession number AAC7701 1) D311E mutation can be used to remove limitations on the pool of acyl-CoA.
In addition, over-expression of an sfa gene (suppressor of FabA, for example Accession number AAN79592) can be included in the production host to increase production of monounsaturated fatty acids (Rock et al., J. Bacteriology 178:5382-5387, 1996).
B. Acyl-ACP to Fatty Acid
To engineer a production host for the production of a homogeneous population of fatty acid derivatives, one or more endogenous genes can be attenuated or functionally deleted and one or more thioesterases can be expressed. For example, C10 fatty acid derivatives can be produced by attenuating thioesterase C18 (for example accession numbers AAC73596 and POADAI), which uses C18:1-ACP and expressing thioesterase C10 (for example accession number Q39513), which uses C10-ACP. Thus, resulting in a relatively homogeneous population of fatty acid derivatives that have a carbon chain length of 10. In another example, C14 fatty acid derivatives can be produced by attenuating endogenous thioesterases that produce non-C14 fatty acids and expressing the thioesterase accession number Q39473 (which uses C14-ACP). In yet another example, C12 fatty acid derivatives can be produced by expressing thioesterases that use C12-ACP (for example accession number Q41635) and attenuating thioesterases that produce non-C12 fatty acids. Acetyl CoA, malonyl CoA, and fatty acid overproduction can be verified using methods known in the art, for example by using radioactive precursors, HPLC, and GC-MS subsequent to cell lysis.
C. Fatty Acid to Acyl-CoA
Production hosts can be engineered using known peptides to produce fatty acids of various lengths. One method of making fatty acids involves increasing the expression of, or expressing more active forms of, one or more acyl-CoA synthase peptides (EC 2.3.1.86).
As used herein, acyl-CoA synthase includes peptides in enzyme classification number EC 2.3.1.86, as well as any other peptide capable of catalyzing the conversion of a fatty acid to acyl-CoA. Additionally, one of ordinary skill in the art will appreciate that some acyl-CoA synthase peptides will catalyze other reactions as well, for example some acyl-CoA synthase peptides will accept other substrates in addition to fatty acids. Such non-specific acyl-CoA synthase peptides are, therefore, also included. Acyl-CoA synthase peptide sequences are publicly available. Exemplary GenBank Accession Numbers are provided in
D. Acyl-CoA to Fatty Alcohol
Production hosts can be engineered using known polypeptides to produce fatty alcohols from acyl-CoA. One method of making fatty alcohols involves increasing the expression of or expressing more active forms of fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), or acyl-CoA reductases (EC 1.2.1.50) and alcohol dehydrogenase (EC 1.1.1.1). Hereinafter fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), acyl-CoA reductases (EC 1.2.1.50) and alcohol dehydrogenase (EC 1.1.1.1) are collectively referred to as fatty alcohol forming peptides. In some examples all three of the fatty alcohol forming genes can be over expressed in a production host, and in yet other examples one or more of the fatty alcohol forming genes can be over-expressed.
As used herein, fatty alcohol forming peptides include peptides in enzyme classification numbers EC 1.1.1.*, 1.2.1.50, and 1.1.1.1, as well as any other peptide capable of catalyzing the conversion of acyl-CoA to fatty alcohol. Additionally, one of ordinary skill in the art will appreciate that some fatty alcohol forming peptides will catalyze other reactions as well, for example some acyl-CoA reductase peptides will accept other substrates in addition to fatty acids. Such non-specific peptides are, therefore, also included. Fatty alcohol forming peptides sequences are publicly available. Exemplary GenBank Accession Numbers are provided in
Fatty alcohols can also be described as hydrocarbon-based surfactants. For surfactant production the microorganism is modified so that it produces a surfactant from a renewable carbon source. Such a microorganism includes a first exogenous DNA sequence encoding a protein capable of converting a fatty acid to a fatty aldehyde and a second exogenous DNA sequence encoding a protein capable of converting a fatty aldehyde to an alcohol. In some examples, the first exogenous DNA sequence encodes a fatty acid reductase. In one embodiment, the second exogenous DNA sequence encodes mammalian microsomal aldehyde reductase or long-chain aldehyde dehydrogenase. In a further example, the first and second exogenous DNA sequences are from a multienzyme complex from Arthrobacter AK 19, Rhodotorula glutinins, Acinobacter sp strain. M-1, or Candida lipolytica. In one embodiment, the first and second heterologous DNA sequences are from a multienzyme complex from Acinobacter sp strain M-1 or Candida lipolytica.
Additional sources of heterologous DNA sequences encoding fatty acid to long chain alcohol converting proteins that can be used in surfactant production include, but are not limited to, Mortierella alpina (ATCC 32222), Crytococcus curvatus, (also referred to as Apiotricum curvatum), Alcanivorax jadensis (T9T=DSM 12718=ATCC 700854), Acinetobacter sp. HO1-N, (ATCC 14987) and Rhodococcus opacus (PD630 DSMZ 44193).
In one example, the fatty acid derivative is a saturated or unsaturated surfactant product having a carbon atom content limited to between 6 and 36 carbon atoms. In another example, the surfactant product has a carbon atom content limited to between 24 and 32 carbon atoms.
Appropriate hosts for producing surfactants can be either eukaryotic or prokaryotic microorganisms. Exemplary hosts include Arthrobacter AK 19, Rhodotorula glutinins, Acinobacter sp strain M-1, Arabidopsis thalania, or Candida lipolytica , Saccharomyces cerevisiae, and E. coli engineered to express acetyl CoA carboxylase. Hosts which demonstrate an innate ability to synthesize high levels of surfactant precursors in the form of lipids and oils, such as Rhodococcus opacus, Arthrobacter AK 19, Rhodotorula glutinins E. coli engineered to express acetyl CoA carboxylase, and other oleaginous bacteria, yeast, and fungi can also be used.
E. Fatty Alcohols to Fatty Esters
Production hosts can be engineered using known polypeptides to produce fatty esters of various lengths. One method of making fatty esters includes increasing the expression of, or expressing more active forms of, one or more alcohol O-acetyltransferase peptides (EC 2.3.1.84). These peptides catalyze the reaction of acetyl-CoA and an alcohol to form CoA and an acetic ester. In some examples the alcohol O-acetyltransferase peptides can be expressed in conjunction with selected thioesterase peptides, FAS peptides and fatty alcohol forming peptides, thus, allowing the carbon chain length, saturation and degree of branching to be controlled. In some cases the bkd operon can be coexpressed to enable branched fatty acid precursors to be produced.
As used herein, alcohol O-acetyltransferase peptides include peptides in enzyme classification number EC 2.3.1.84, as well as any other peptide capable of catalyzing the conversion of acetyl-CoA and an alcohol to form CoA and an acetic ester. Additionally, one of ordinary skill in the art will appreciate that alcohol O-acetyltransferase peptides will catalyze other reactions as well, for example some alcohol O-acetyltransferase peptides will accept other substrates in addition to fatty alcohols or acetyl-CoA thiosester i.e., such as other alcohols and other acyl-CoA thioesters. Such non-specific or divergent specificity alcohol O-acetyltransferase peptides are, therefore, also included. Alcohol O-acetyltransferase peptide sequences are publicly available. Exemplary GenBank Accession Numbers are provided in
F. Acyl-CoA to Fatty Esters (Biodiesels and Waxes)
Production hosts can be engineered using known peptides to produce fatty acid esters from acyl-CoA and alcohols. In some examples the alcohols are provided in the fermentation media and in other examples the production host can provide the alcohol as described herein. One of ordinary skill in the art will appreciate that structurally, fatty acid esters have an A and a B side. As described herein, the A side of the ester is used to describe the carbon chain contributed by the alcohol, and the B side of the ester is used to describe the carbon chain contributed by the acyl-CoA. Either chain can be saturated or unsaturated, branched or unbranched. The production host can be engineered to produce fatty alcohols or short chain alcohols. The production host can also be engineered to produce specific acyl-CoA molecules. As used herein fatty acid esters are esters derived from a fatty acyl-thioester and an alcohol, wherein the A side and the B side of the ester can vary in length independently. Generally, the A side of the ester is at least 1, 2, 3, 4, 5, 6, 7, or 8 carbons in length, while the B side of the ester is 8, 10, 12, 14, 16, 18, 20, 22, 24, or 26 carbons in length. The A side and the B side can be straight chain or branched, saturated or unsaturated.
The production of fatty esters, including waxes from acyl-CoA and alcohols can be engineered using known polypeptides. As used herein waxes are long chain fatty acid esters, wherein the A side and the B side of the ester can vary in length independently. Generally, the A side of the ester is at least 8, 10, 12, 14, 16, 18, 20, 22, 24, or 26 carbons in length. Similarly the B side of the ester is at least 8, 10, 12, 14, 16, 18, 20, 22, 24, or 26 carbons in length. The A side and the B side can be mono-, di-, tri- unsaturated. The production of fatty esters, including waxes from acyl-CoA and alcohols can be engineered using known polypeptides. One method of making fatty esters includes increasing the expression of or expressing more active forms of one or more wax synthases (EC 2.3.1.75).
As used herein, wax synthases includes peptides in enzyme classification number EC 2.3.1.75, as well as any other peptide capable of catalyzing the conversion of an acyl-thioester to fatty esters. Additionally, one of ordinary skill in the art will appreciate that some wax synthase peptides will catalyze other reactions as well, for example some wax synthase peptides will accept short chain acyl-CoAs and short chain alcohols to produce fatty esters. Such non-specific wax synthases are, therefore, also included. Wax synthase peptide sequences are publicly available. Exemplary GenBank Accession Numbers are provided in
In particular examples, if the desired product is a fatty ester based biofuel, the microorganism is modified so that it produces a fatty ester generated from a renewable energy source. Such a microorganism includes an exongenous DNA sequence encoding a wax ester synthase that is expressed so as to confer upon said microorganism the ability to synthesize a saturated, unsaturated, or branched fatty ester from a renewable energy source. In some embodiments, the wax ester synthesis proteins include, but are not limited to,: fatty acid elongases, acyl-CoA reductases, acyltransferases or wax synthases, fatty acyl transferases, diacylglycerol acyltransferases, acyl-coA wax alcohol acyltransferases, bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase selected from a multienzyme complex from Simmondsia chinensis, Acinetobacter sp. strain ADP1 (formerly Acinetobacter calcoaceticus ADP1), Pseudomonas aeruginosa, Fundibacter jadensis, Arabidopsis thaliana, or Alkaligenes eutrophus. In one embodiment, the fatty acid elongases, acyl-CoA reductases or wax synthases are from a multienzyme complex from Alkaligenes eutrophus and other organisms known in the literature to produce wax and fatty acid esters.
Additional sources of heterologous DNA encoding wax synthesis proteins useful in fatty ester production include, but are not limited to, Mortierella alpina (for example ATCC 32222), Crytococcus curvatus, (also referred to as Apiotricwn curvatum), Alcanivorax jadensis (for example T9T=DSM 12718=ATCC 700854), Acinetobacter sp. HO1-N, (for example ATCC 14987) and Rhodococcus opacus (for example PD630, DSMZ 44193).
The methods of described herein permit production of fatty esters of varied length. In one example, the fatty ester product is a saturated or unsaturated fatty ester product having a carbon atom content between 24 and 46 carbon atoms. In one embodiment, the fatty ester product has a carbon atom content between 24 and 32 carbon atoms. In another embodiment the fatty ester product has a carbon content of 14 and 20 carbons. In another embodiment the fatty ester is the methyl ester of C18:1. In another embodiment the fatty acid ester is the ethyl ester of C16:1. In another embodiment the fatty ester is the methyl ester of C16:1. In another embodiment the fatty acid ester is octadecyl ester of octanol.
Useful hosts for producing fatty esters can be either eukaryotic or prokaryotic microorganisms. In some embodiments such hosts include, but are not limited to, Saccharomyces cerevisiae, Candida lipolytica, E. coli, Arthrobacter AK 19, Rhodotorula glutinins, Acinobacter sp strain M-1, Candida lipolytica and other oleaginous microorganisms.
In one example the wax ester synthase from Acinetobacter sp. ADP1 at locus AAO17391 (described in Kalscheuer and Steinbuchel, J. Biol. Chem. 278:8075-8082, 2003, herein incorporated by reference) is used. In another example the wax ester synthase from Simmondsia chinensis, at locus AAD38041 is used.
Optionally a wax ester exporter such as a member of the FATP family can be used to facilitate the release of waxes or esters into the extracellular environment. One example of a wax ester exporter that can be used is fatty acid (long chain) transport protein CG7400-PA, isoform A from Drosophila melanogaster, at locus NP—524723.
G. Acyl-ACP, Acyl-CoA to Hydrocarbon
A diversity of microorganisms are known to produce hydrocarbons, such as alkanes, olefins, and isoprenoids. Many of these hydrocarbons are derived from fatty acid biosynthesis. The production of these hydrocarbons can be controlled by controlling the genes associated with fatty acid biosynthesis in the native hosts. For example, hydrocarbon biosynthesis in the algae Botryococcus braunii occurs through the decarbonylation of fatty aldehydes. The fatty aldehydes are produced by the reduction of fatty acyl—thioesters by fatty acyl-CoA reductase. Thus, the structure of the final alkanes can be controlled by engineering B. braunii to express specific genes, such as thioesterases, which control the chain length of the fatty acids being channeled into alkane biosynthesis. Expressing the enzymes that result in branched chain fatty acid biosynthesis in B. braunii will result in the production of branched chain alkanes. Introduction of genes effecting the production of desaturation of fatty acids will result in the production of olefins. Further combinations of these genes can provide further control over the final structure of the hydrocarbons produced. To produce higher levels of the native or engineered hydrocarbons, the genes involved in the biosynthesis of fatty acids and their precursors or the degradation to other products can be expressed, overexpressed, or attenuated. Each of these approaches can be applied to the production of alkanes in Vibrio furnissi M1 and its functional homologues, which produces alkanes through the reduction of fatty alcohols (see above for the biosynthesis and engineering of fatty alcohol production). Each of these approaches can also be applied to the production of the olefins produced by many strains of Micrococcus leuteus, Stenotrophomonas maltophilia, Jeogalicoccus sp. (ATCC8456), and related microorganisms. These microorganisms produce long chain internal olefins that are derived from the head to head condensation of fatty acid precursors. Controlling the structure and level of the fatty acid precursors using the methods described herein will result in formation of olefins of different chain length, branching, and level of saturation.
Hydrocarbons can also be produced using evolved oxido/reductases for the reduction of primary alcohols. Primary fatty alcohols are known to be used to produce alkanes in microorganisms such as Vibrio furnissii M1 (Myong-Ok, J. Bacteriol., 187:1426-1429, 2005). An NAD(P)H dependent oxido/reductase is the responsible catalyst. Synthetic NAD(P)H dependent oxidoreductases can be produced through the use of evolutionary engineering and be expressed in production hosts to produce fatty acid derivatives. One of ordinary skill in the art will appreciate that the process of “evolving” a fatty alcohol reductase to have the desired activity is well known (Kolkman and Stemmer Nat Biotechnol. 19:423-8, 2001, Ness et al., Adv Protein Chem. 55:261-92, 2000, Minshull and Stemmer Curr Opin Chem Biol. 3:284-90, 1999, Huisman and Gray Curr Opin Biotechnol. August;13:352-8, 2002, and see U.S. patent application 2006/0195947). A library of NAD(P)H dependent oxidoreductases is generated by standard methods, such as error prone PCR, site-specific random mutagenesis, site specific saturation mutagenesis, or site directed specific mutagenesis. Additionally, a library can be created through the “shuffling” of naturally occurring NAD(P)H dependent oxidoreductase encoding sequences. The library is expressed in a suitable host, such as E. coli. Individual colonies expressing a different member of the oxido/reductase library is then analyzed for its expression of an oxido/reductase that can catalyze the reduction of a fatty alcohol. For example, each cell can be assayed as a whole cell bioconversion, a cell extract, a permeabilized cell, or a purified enzyme. Fatty alcohol reductases are identified by the monitoring the fatty alcohol dependent oxidation of NAD(P)H spectrophotometrically or fluorometrically. Production of alkanes is monitored by GC/MS, TLC, or other methods. An oxido/reductase identified in this manner is used to produce alkanes, alkenes, and related branched hydrocarbons. This is achieved either in vitro or in vivo. The latter is achieved by expressing the evolved fatty alcohol reductase gene in an organism that produces fatty alcohols, such as those described herein. The fatty alcohols act as substrates for the alcohol reductase which would produce alkanes. Other oxidoreductases can be also engineered to catalyze this reaction, such as those that use molecular hydrogen, glutathione, FADH, or other reductive coenzymes.
II. Genetic Engineering of Production Strain to increase Fatty Acid Derivative Production
Heterologous DNA sequences involved in a biosynthetic pathway for the production of fatty acid derivatives can be introduced stably or transiently into a host cell using techniques well known in the art for example electroporation, calcium phosphate precipitation, DEAE-dextran mediated transfection, liposome-mediated transfection, conjugation, transduction, and the like. For stable transformation, a DNA sequence can further include a selectable marker, such as, antibiotic resistance, for example resistance to neomycin, tetracycline, chloramphenicol, kanamycin, genes that complement auxotrophic deficiencies, and the like.
Various embodiments of this disclosure utilize an expression vector that includes a heterologous DNA sequence encoding a protein involved in a metabolic or biosynthetic pathway. Suitable expression vectors include, but are not limited to, viral vectors, such as baculovirus vectors, phage vectors, such as bacteriophage vectors, plasmids, phagemids, cosmids, fosmids, bacterial artificial chromosomes, viral vectors (e.g. viral vectors based on vaccinia virus, poliovirus, adenovirus, adeno-associated virus, SV40, herpes simplex virus, and the like), P1-based artificial chromosomes, yeast plasmids, yeast artificial chromosomes, and any other vectors specific for specific hosts of interest (such as E. coli, Pseudomonas pisum and Saccharomyces cerevisiae).
Useful expression vectors can include one or more selectable marker genes to provide a phenotypic trait for selection of transformed host cells. The selectable marker gene encodes a protein necessary for the survival or growth of transformed host cells grown in a selective culture medium. Host cells not transformed with the vector containing the selectable marker gene will not survive in the culture medium. Typical selection genes encode proteins that (a) confer resistance to antibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate, or tetracycline, (b) complement auxotrophic deficiencies, or (c) supply critical nutrients not available from complex media, e.g., the gene encoding D-alanine racemase for Bacilli. In alternative embodiments, the selectable marker gene is one that encodes dihydrofolate reductase or confers neomycin resistance (for use in eukaryotic cell culture), or one that confers tetracycline or ampicillin resistance (for use in a prokaryotic host cell, such as E. coli).
The biosynthetic pathway gene product-encoding DNA sequence in the expression vector is operably linked to an appropriate expression control sequence, (promoters, enhancers, and the like) to direct synthesis of the encoded gene product. Such promoters can be derived from microbial or viral sources, including CMV and SV40. Depending on the host/vector system utilized, any of a number of suitable transcription and translation control elements, including constitutive and inducible promoters, transcription enhancer elements, transcription terminators, etc. can be used in the expression vector (see e.g., Bitter et al., Methods in Enzymology, 153:516-544, 1987).
Suitable promoters for use in prokaryotic host cells include, but are not limited to, promoters capable of recognizing the T4, T3, Sp6 and T7 polymerases, the PR and PL promoters of bacteriophage lambda, the trp, recA, heat shock, and lacZ promoters of E. coli, the alpha-amylase and the sigma-specific promoters of B. subtilis, the promoters of the bacteriophages of Bacillus, Streptomyces promoters, the int promoter of bacteriophage lambda, the bla promoter of the beta-lactamase gene of pBR322, and the CAT promoter of the chloramphenicol acetyl transferase gene. Prokaryotic promoters are reviewed by Glick, J. Ind. Microbiol. 1:277, 1987; Watson et al., MOLECULAR BIOLOGY OF THE GENE, 4th Ed., Benjamin Cummins (1987); and Sambrook et al., supra.
Non-limiting examples of suitable eukaryotic promoters for use within a eukaryotic host are viral in origin and include the promoter of the mouse metallothionein I gene (Hamer et al., J. Mol. Appl. Gen. 1:273, 1982); the TK promoter of Herpes virus (McKnight, Cell 31:355, 1982); the SV40 early promoter (Benoist et al., Nature (London) 290:304, 1981); the Rous sarcoma virus promoter; the cytomegalovirus promoter (Foecking et al., Gene 45:101, 1980); the yeast gal4 gene promoter (Johnston, et al., PNAS (USA) 79:6971, 1982; Silver, et al., PNAS (USA) 81:5951, 1984); and the IgG promoter (Orlandi et al., PNAS (USA) 86:3833, 1989).
The microbial host cell can be genetically modified with a heterologous DNA sequence encoding a biosynthetic pathway gene product that is operably linked to an inducible promoter. Inducible promoters are well known in the art. Suitable inducible promoters include, but are not limited to promoters that are affected by proteins, metabolites, or chemicals. These include: a bovine leukemia virus promoter, a metallothionein promoter, a dexamethasone-inducible MMTV promoter, a SV40 promoter, a MRP polIII promoter, a tetracycline-inducible CMV promoter (such as the human immediate-early CMV promoter) as well as those from the trp and lac operons.
In some examples a genetically modified host cell is genetically modified with a heterologous DNA sequence encoding a biosynthetic pathway gene product that is operably linked to a constitutive promoter. Suitable constitutive promoters are known in the art and include, constitutive adenovirus major late promoter, a constitutive MPSV promoter, and a constitutive CMV promoter.
In some examples a modified host cell is one that is genetically modified with an exongenous DNA sequence encoding a single protein involved in a biosynthesis pathway.
In other embodiments, a modified host cell is one that is genetically modified with exongenous DNA sequences encoding two or more proteins involved in a biosynthesis pathway--for example, the first and second enzymes in a biosynthetic pathway.
Where the host cell is genetically modified to express two or more proteins involved in a biosynthetic pathway, those DNA sequences can each be contained in a single or in separate expression vectors. When those DNA sequences are contained in a single expression vector, in some embodiments, the nucleotide sequences will be operably linked to a common control element (e.g., a promoter), e.g., the common control element controls expression of all of the biosynthetic pathway protein-encoding DNA sequences in the single expression vector.
When a modified host cell is genetically modified with heterologous DNA sequences encoding two or more proteins involved in a biosynthesis pathway, one of the DNA sequences can be operably linked to an inducible promoter, and one or more of the DNA sequences can be operably linked to a constitutive promoter.
In some embodiments, the intracellular concentration (e.g., the concentration of the intermediate in the genetically modified host cell) of the biosynthetic pathway intermediate can be increased to further boost the yield of the final product. The intracellular concentration of the intermediate can be increased in a number of ways, including, but not limited to, increasing the concentration in the culture medium of a substrate for a biosynthetic pathway; increasing the catalytic activity of an enzyme that is active in the biosynthetic pathway; increasing the intracellular amount of a substrate (e.g., a primary substrate) for an enzyme that is active in the biosynthetic pathway; and the like.
In some examples the fatty acid derivative or intermediate is produced in the cytoplasm of the cell. The cytoplasmic concentration can be increased in a number of ways, including, but not limited to, binding of the fatty acid to coenzyme A to form an acyl-CoA thioester. Additionally, the concentration of acyl-CoAs can be increased by increasing the biosynthesis of CoA in the cell, such as by over-expressing genes associated with pantothenate biosynthesis (panD) or knocking out the genes associated with glutathione biosynthesis (glutathione synthase).
III. Carbon Chain CharacteristicsUsing the teachings provided herein a range of products can be produced. These products include hydrocarbons, fatty alcohols, fatty acid esters, and waxes. Some of these products are useful as biofuels and specialty chemicals. These products can be designed and produced in microorganisms. The products can be produced such that they contain branch points, levels of saturation, and carbon chain length, thus, making these products desirable starting materials for use in many applications (
In other examples, the expression of exongenous FAS genes originating from different species or engineered variants can be introduced into the host cell to result in the biosynthesis of fatty acid metabolites structurally different (in length, branching, degree of unsaturation, etc.) as that of the native host. These heterologous gene products can be also chosen or engineered so that they are unaffected by the natural complex regulatory mechanisms in the host cell and, therefore, function in a manner that is more controllable for the production of the desired commercial product. For example the FAS enzymes from Bacillus subtilis, Saccharomyces cerevisiae, Streptomyces spp, Ralstonia, Rhodococcus, Corynebacteria, Brevibacteria, Mycobacteria, oleaginous yeast, and the like can be expressed in the production host.
One of ordinary skill in the art will appreciate that when a production host is engineered to produce a fatty acid from the fatty acid biosynthetic pathway that contains a specific level of unsaturation, branching, or carbon chain length the resulting engineered fatty acid can be used in the production of the fatty acid derivatives. Hence, fatty acid derivatives generated from the production host can display the characteristics of the engineered fatty acid. For example, a production host can be engineered to make branched, short chain fatty acids, and then using the teachings provided herein relating to fatty alcohol production (i.e. including alcohol forming enzymes such as FAR) the production host produce branched, short chain fatty alcohols. Similarly, a hydrocarbon can be produced by engineering a production host to produce a fatty acid having a defined level of branching, unsaturation, and/or carbon chain length, thus, producing a homogenous hydrocarbon population. Moreover, when an unsaturated alcohol, fatty acid ester, or hydrocarbon is desired the fatty acid biosynthetic pathway can be engineered to produce low levels of saturated fatty acids and an additional desaturase can be expressed to lessen the saturated product production.
A. Saturation
Production hosts can be engineered to produce unsaturated fatty acids by engineering the production host to over-express fabB, or by growing the production host at low temperatures (for example less than 37° C.). FabB has preference to cis-δ3decenoyl-ACP and results in unsaturated fatty acid production in E. coli. Over-expression of FabB resulted in the production of a significant percentage of unsaturated fatty acids (de Mendoza et al., J. Biol. Chem., 258:2098-101, 1983). These unsaturated fatty acids can then be used as intermediates in production hosts that are engineered to produce fatty acid derivatives, such as fatty alcohols, esters, waxes, olefins, alkanes, and the like. One of ordinary skill in the art will appreciate that by attenuating fabA, or over-expressing FabB and expressing specific thioesterases (described below), unsaturated fatty acid derivatives having a desired carbon chain length can be produced. Alternatively, the repressor of fatty acid biosynthesis, FabR (Genbank accession NP—418398), can be deleted, which will also result in increased unsaturated fatty acid production in E. coli (Zhang et al., J. Biol. Chem. 277:pp. 15558, 2002.). Further increase in unsaturated fatty acids may be achieved by over-expression of FabM (trans-2, cis-3-decenoyl-ACP isomerase, Genbank accession DAA05501) and controlled expression of FabK (trans-2-enoyl-ACP reductase II, Genbank accession NP—357969) from Streptococcus pneumoniae (Marrakchi et al., J. Biol. Chem. 277: 44809, 2002), while deleting E. coli Fab I ((trans-2-enoyl-ACP reductase, Genbank accession NP—415804). Additionally, to increase the percentage of unsaturated fatty acid esters, the microorganism can also have fabB (encoding β-ketoacyl-ACP synthase I, Accessions: BAA16180, EC:2.3.1.41), Sfa (encoding a suppressor of fabA, Accession: AAC44390) and gnsA and gnsB (both encoding secG null mutant suppressors, a.k.a. cold shock proteins, Accession: ABD18647.1, AAC74076.1) over-expressed.
In some examples, the endogenous fabF gene can be attenuated, thus, increasing the percentage of palmitoleate (C16:1) produced.
B. Branching Including Cyclic Moieties
Fatty acid derivatives can be produced that contain branch points, cyclic moieties, and combinations thereof, using the teachings provided herein.
Microorganisms that naturally produce straight fatty acids (sFAs) can be engineered to produce branched chain fatty acids (brFAs) by expressing one or more exogenous nucleic acid sequences. For example, E. coli naturally produces straight fatty acids (sFAs). To engineer E. coli to produce brFAs, several genes can be introduced and expressed that provide branched precursors (bkd operon) and allow initiation of fatty acid biosynthesis from branched precursors (fabH). Additionally, the organism can express genes for the elongation of brFAs (e.g. ACP, FabF) and/or deleting the corresponding E. coli genes that normally lead to sFAs and would compete with the introduced genes (e.g. FabH, FabF).
The branched acyl-CoAs 2-methyl-buturyl-CoA, isovaleryl-CoA and isobuturyl-CoA are the precursors of brFA. In most brFA-containing microorganisms they are synthesized in two steps (described in detail below) from branched amino acids (isoleucine, leucine and valine) (Kadena, Microbiol. Rev. 55: pp. 288, 1991). To engineer a microorganism to produce brFAs, or to overproduce brFAs, expression or over-expression of one or more of the enzymes in these two steps can be engineered. For example, in some instances the production host may have an endogenous enzyme that can accomplish one step and therefore, only enzymes involved in the second step need to be expressed recombinantly.
The first step in forming branched fatty acids is the production of the corresponding α-keto acids by a branched-chain amino acid aminotransferase. E. coli has such an enzyme, IlvE (EC 2.6.1.42; Genbank accession YP—026247). In some examples, a heterologous branched-chain amino acid aminotransferase may not be expressed. However, E. coli IlvE or any other branched-chain amino acid aminotransferase, e.g. ilvE from Lactococcus lactis (Genbank accession AAF34406), ilvE from Pseudomonas putida (Genbank accession NP—745648) or ilvE from Streptomyces coelicolor (Genbank accession NP—629657) can be over-expressed in a host microorganism, should the aminotransferase reaction turn out to be rate limiting in brFA biosynthesis in the host organism chosen for fatty acid derivative production.
The second step, the oxidative decarboxylation of the α-ketoacids to the corresponding branched-chain acyl-CoA, is catalyzed by a branched-chain α-keto acid dehydrogenase complexes (bkd; EC 1.2.4.4.) (Denoya et al. J. Bacteriol. 177:pp. 3504, 1995), which consist of E1α/β (decarboxylase), E2 (dihydrolipoyl transacylase) and E3 (dihydrolipoyl dehydrogenase) subunits and are similar to pyruvate and α-ketoglutarate dehydrogenase complexes. Table 2 shows potential bkd genes from several microorganisms, that can be expressed in a production host to provide branched-chain acyl-CoA precursors. Basically, every microorganism that possesses brFAs and/or grows on branched-chain amino acids can be used as a source to isolate bkd genes for expression in production hosts such as, for example, E. coli. Furthermore, E. coli has the E3 component (as part of its pyruvate dehydrogenase complex; 1pd, EC 1.8.1.4, Genbank accession NP—414658), it can therefore, be sufficient to only express the E1α/β and E2 bkd genes.
In another example, isobuturyl-CoA can be made in a production host, for example in E. coli through the coexpression of a crotonyl-CoA reductase (Ccr, EC 1.1.1.9) and isobuturyl-CoA mutase (large subunit IcmA, EC 5.4.99.2; small subunit IcmB, EC 5.4.99.13) (Han and Reynolds J. Bacteriol. 179:pp. 5157, 1997). Crotonyl-CoA is an intermediate in fatty acid biosynthesis in E. coli and other microorganisms. Examples for ccr and icm genes from selected microorganisms are given in Table 3.
In addition to expression of the bkd genes (see above), the initiation of brFA biosynthesis utilizes β-ketoacyl-acyl-carrier-protein synthase III (FabH, EC 2.3.1.41) with specificity for branched chain acyl CoAs (Li et al. J. Bacteriol. 187:pp. 3795, 2005). Examples of such FabHs are listed in Table 4. FabH genes that are involved in fatty acid biosynthesis of any brFA-containing microorganism can be expressed in a production host. The Bkd and FabH enzymes from production hosts that do not naturally make brFA may not support brFA production and therefore, Bkd and FabH can be expressed recombinantly. Similarly, the endogenous level of Bkd and FabH production may not be sufficient to produce brFA, therefore, they can be over-expressed. Additionally, other components of fatty acid biosynthesis machinery can be expressed such as acyl carrier proteins (ACPs) and β-ketoacyl-acyl-carrier-protein synthase II candidates are acyl carrier proteins (ACPs) and β-ketoacyl-acyl-carrier-protein synthase II (fabF, EC 2.3.1.41) (candidates are listed in Table 4). In addition to expressing these genes, some genes in the endogenous fatty acid biosynthesis pathway may be attenuated in the production host. For example, in E. coli the most likely candidates to interfere with brFA biosynthesis are fabH (Genbank accession # NP—415609) and/or fabF genes (Genbank accession #NP—415613).
As mentioned above, through the combination of expressing genes that support brFA synthesis and alcohol synthesis branched chain alcohols can be produced. For example, when an alcohol reductase such as Acrl from Acinetobacter baylyi ADP1 is coexpressed with a bkd operon, E. coli can synthesize isopentanol, isobutanol or 2-methyl butanol. Similarly, when Acr1 is coexpressed with ccr/icm genes, E. coli can synthesize isobutanol.
In order to convert a production host such as E. coli into an organism capable of synthesizing co-cyclic fatty acids (cyFAs), several genes need to be introduced and expressed that provide the cyclic precursor cyclohexylcarbonyl-CoA (Cropp et al. Nature Biotech. 18:pp. 980, 2000). The genes listed in Table 4 (fabH, ACP and fabF) can then be expressed to allow initiation and elongation of ω-cyclic fatty acids. Alternatively, the homologous genes can be isolated from microorganisms that make cyFAs and expressed in E. coli.
Expression of the following genes are sufficient to provide cyclohexylcarbonyl-CoA in E. coli: ansJ, ansK, ansL, chcA and ansM from the ansatrienin gene cluster of Streptomyces collinus (Chen et al., Eur. J. Biochem. 261:pp. 1999, 1999) or plmJ, plmL, chcA and plmM from the phoslactomycin B gene cluster of Streptomyces sp. HK803 (Palaniappan et al., J. Biol. Chem. 278:pp. 35552, 2003) together with the chcB gene (Patton et al. Biochem., 39:pp. 7595, 2000) from S. collinus, S. avermitilis or S. coelicolor (see Table 5 for Genbank accession numbers).
The genes listed in Table 4 (fabH, ACP and fabF) are sufficient to allow initiation and elongation of co-cyclic fatty acids, because they can have broad substrate specificity. In the event that coexpression of any of these genes with the ansJKLM/chcAB or pm1JKLM/chcAB genes from Table 5 does not yield cyFAs,fabH, ACP and/or fabF homologs from microorganisms that make cyFAs can be isolated (e.g. by using degenerate PCR primers or heterologous DNA probes) and coexpressed. Table 6 lists selected microorganisms that contain co-cyclic fatty acids.
C. Ester characteristics
One of ordinary skill in the art will appreciate that an ester includes an A side and a B side. As described herein, the B side is contributed by a fatty acid produced from de novo synthesis in the host organism. In some instances where the host is additionally engineered to make alcohols, including fatty alcohols, the A side is also produced by the host organism. In yet other examples the A side can be provided in the medium. As described herein, by selecting the desired thioesterase genes the B side, and when fatty alcohols are being made the A side, can be designed to be have certain carbon chain characteristics. These characteristics include points of unsaturation, branching, and desired carbon chain lengths. Exemplary methods of making long chain fatty acid esters, wherein the A and B side are produced by the production host are provided in Example 6, below. Similarly, Example 5 provides methods of making medium chain fatty acid esters. When both the A and B side are contributed by the production host and they are produced using fatty acid biosynthetic pathway intermediates they will have similar carbon chain characteristics. For example, at least 50%, 60%, 70%, or 80% of the fatty acid esters produced will have A sides and B sides that vary by 6, 4, or 2 carbons in length. The A side and the B side will also display similar branching and saturation levels.
In addition to producing fatty alcohols for contribution to the A side, the host can produce other short chain alcohols such as ethanol, propanol, isopropanol, isobutanol, and butanol for incorporation on the A side using techniques well known in the art. For example, butanol can be made by the host organism. To create butanol producing cells, the LS9001 strain (described in Example 1, below) can be further engineered to express atoB (acetyl-CoA acetyltransferase) from Escherichia coli K12, β-hydroxybutyryl-CoA dehydrogenase from Butyrivibrio fibrisolvens, crotonase from Clostridium beijerinckii, butyryl CoA dehydrogense from Clostridium beijerinckii, CoA-acylating aldehyde dehydrogenase (ALDH) from Cladosporium fulvum, and adhE encoding an aldehyde-alchol dehydrogenase of Clostridium acetobutylicum in the pBAD24 expression vector under the prpBCDE promoter system. Similarly, ethanol can be produced in a production host using the methods taught by Kalscheuer et al., Microbiology 152:2529-2536, 2006, which is herein incorporated by reference.
IV. FermentationThe production and isolation of fatty acid derivatives can be enhanced by employing specific fermentation techniques. One method for maximizing production while reducing costs is increasing the percentage of the carbon source that is converted to hydrocarbon products. During normal cellular lifecycles carbon is used in cellular functions including producing lipids, saccharides, proteins, organic acids, and nucleic acids. Reducing the amount of carbon necessary for growth-related activities can increase the efficiency of carbon source conversion to output. This can be achieved by first growing microorganisms to a desired density, such as a density achieved at the peak of the log phase of growth. At such a point, replication checkpoint genes can be harnessed to stop the growth of cells. Specifically, quorum sensing mechanisms (reviewed in Camilli and Bassler Science 311:1113, 2006; Venturi FEMS Microbio Rev 30:274-291, 2006; and Reading and Sperandio FEMS Microbiol Lett 254:1-11, 2006) can be used to activate genes such as p53, p21, or other checkpoint genes. Genes that can be activated to stop cell replication and growth in E. coli include umuDC genes, the over-expression of which stops the progression from stationary phase to exponential growth (Murli et al., J. of Bact. 182:1127, 2000). UmuC is a DNA polymerase that can carry out translesion synthesis over non-coding lesions--the mechanistic basis of most UV and chemical mutagenesis. The umuDC gene products are used for the process of translesion synthesis and also serve as a DNA damage checkpoint. UmuDC gene products include UmuC, UmuD, umuD′, UmuD′, UmuD′2C, UmuD′2 and UmuD2. Simultaneously, the product producing genes would be activated, thus minimizing the need for replication and maintenance pathways to be used while the fatty acid derivative is being made.
The percentage of input carbons converted to hydrocarbon products is a cost driver. The more efficient (i.e. the higher the percentage), the less expensive the process. For oxygen-containing carbon sources (i.e. glucose and other carbohydrate based sources), the oxygen must be released in the form of carbon dioxide. For every 2 oxygen atoms released, a carbon atom is also released leading to a maximal theoretical metabolic efficiency of about 34% (w/w) (for fatty acid derived products). This figure, however, changes for other hydrocarbon products and carbon sources. Typical efficiencies in the literature are about <5%. Engineered microorganisms which produce hydrocarbon products can have greater than 1, 3, 5, 10, 15, 20, 25, and 30% efficiency. In one example microorganisms will exhibit an efficiency of about 10% to about 25%. In other examples, such microorganisms will exhibit an efficiency of about 25% to about 30%, and in other examples such microorganisms will exhibit >30% efficiency.
In some examples where the final product is released from the cell, a continuous process can be employed. In this approach, a reactor with organisms producing fatty acid derivatives can be assembled in multiple ways. In one example, a portion of the media is removed and let to sit. Fatty acid derivatives are separated from the aqueous layer, which will in turn, be returned to the fermentation chamber.
In one example, the fermentation chamber will enclose a fermentation that is undergoing a continuous reduction. In this instance, a stable reductive environment would be created. The electron balance would be maintained by the release of carbon dioxide (in gaseous form). Efforts to augment the NAD/H and NADP/H balance can also facilitate in stabilizing the electron balance.
The availability of intracellular NADPH can be also enhanced by engineering the production host to express an NADH:NADPH transhydrogenase. The expression of one or more NADH:NADPH transhydrogenase converts the NADH produced in glycolysis to NADPH which enhances the production of fatty acid derivatives.
Disclosed herein is a system for continuously producing and exporting fatty acid derivatives out of recombinant host microorganisms via a transport protein. Many transport and efflux proteins serve to excrete a large variety of compounds and can be evolved to be selective for a particular type of fatty acid derivatives. Thus, in some embodiments an exogenous DNA sequence encoding an ABC transporter will be functionally expressed by the recombinant host microorganism, so that the microorganism exports the fatty acid derivative into the culture medium. In one example, the ABC transporter is an ABC transporter from Caenorhabditis elegans, Arabidopsis thalania, Alkaligenes eutrophus or Rhodococcus erythropolis (locus AAN73268). In another example, the ABC transporter is an ABC transporter chosen from CER5 (locuses At1g51500 or AY734542), AtMRP5, AmiS2 and AtPGPI. In some examples, the ABC transporter is CER5. In yet another example, the CER5 gene is from Arabidopsis (locuses At1g51500, AY734542, At3g21090 and At1g51460).
The transport protein, for example, can also be an efflux protein selected from: AcrAB, TolC and AcrEF from E. coli, or tll1618, tll1619 and tll0139 from Thermosynechococcus elongatus BP-1.
In addition, the transport protein can be, for example, a fatty acid transport protein (FATP) selected from Drosophila melanogaster, Caenorhabditis elegans, Mycobacterium tuberculosis or Saccharomyces cerevisiae or any one of the mammalian FATP's. The FATPs can additionally be resynthesized with the membranous regions reversed in order to invert the direction of substrate flow. Specifically, the sequences of amino acids composing the hydrophilic domains (or membrane domains) of the protein, could be inverted while maintaining the same codons for each particular amino acid. The identification of these regions is well known in the art.
Production hosts can also be chosen for their endogenous ability to release fatty acid derivatives. The efficiency of product production and release into the fermentation broth can be expressed as a ratio intracellular product to extracellular product. In some examples the ratio can be 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, or 1:5.
The production host can be additionally engineered to express recombinant cellulosomes, such as those described in PCT application number PCT/US2007/003736, which will allow the production host to use cellulosic material as a carbon source. For example, the production host can be additionally engineered to express invertases (EC 3.2.1.26) so that sucrose can be used as a carbon source.
Similarly, the production host can be engineered using the teachings described in U.S. Pat. Nos. 5,000,000, 5,028,539, 5,424,202, 5,482,846, and 5,602,030 to Ingram et al. so that the production host can assimilate carbon efficiently and use cellulosic materials as carbons sources.
IV. Post Production ProcessingThe fatty acid derivatives produced during fermentation can be separated from the fermentation media. Any technique known for separating fatty acid derivatives from aqueous media can be used. One exemplary separation process provided herein is a two phase (bi-phasic) separation process. This process involves fermenting the genetically engineered production hosts under conditions sufficient to produce a fatty acid derivative, allowing the derivative to collect in an organic phase and separating the organic phase from the aqueous fermentation broth. This method can be practiced in both a batch and continuous fermentation setting.
Bi-phasic separation uses the relative immisiciblity of fatty acid derivatives to facilitate separation. Immiscible refers to the relative inability of a compound to dissolve in water and is defined by the compounds partition coefficient. The partition coefficient, P, is defined as the equilibrium concentration of compound in an organic phase (in a bi-phasic system the organic phase is usually the phase formed by the fatty acid derivative during the production process, however, in some examples an organic phase can be provided (such as a layer of octane to facilitate product separation) divided by the concentration at equilibrium in an aqueous phase (i.e. fermentation broth). When describing a two phase system the P is usually discussed in terms of logP. A compound with a logP of 10 would partition 10:1 to the organic phase, while a compound of logP of 0.1 would partition 10:1 to the aqueous phase. One or ordinary skill in the art will appreciate that by choosing a fermentation broth and the organic phase such that the fatty acid derivative being produced has a high logP value, the fatty acid derivative will separate into the organic phase, even at very low concentrations in the fermentation vessel.
The fatty acid derivatives produced by the methods described herein will be relatively immiscible in the fermentation broth, as well as in the cytoplasm. Therefore, the fatty acid derivative will collect in an organic phase either intracellularly or extracellularly. The collection of the products in an organic phase will lessen the impact of the fatty acid derivative on cellular function and will allow the production host to produce more product. Stated another way, the concentration of the fatty acid derivative will not have as significant of an impact on the host cell.
The fatty alcohols, fatty acid esters, waxes, and hydrocarbons produced as described herein allow for the production of Komogeneous compounds wherein at least 60%, 70%, 80%, 90%, or 95% of the fatty alcohols, fatty acid esters, and waxes produced will have carbon chain lengths that vary by less than 4 carbons, or less than 2 carbons. These compounds can also be produced so that they have a relatively uniform degree of saturation, for example at least 60%, 70%, 80%, 90%, or 95% of the fatty alcohols, fatty acid esters, hydrocarbons and waxes will be mono-, di-, or tri-unsaturated. These compounds can be used directly as fuels, personal care additives, nutritional supplements. These compounds can also be used as feedstock for subsequent reactions for example transesterification, hydrogenation, catalytic cracking via either hydrogenation, pyrolisis, or both or epoxidations reactions to make other products.
V. Fuel CompositionsThe fatty acid derivatives described herein can be used as fuel. One of ordinary skill in the art will appreciate that depending upon the intended purpose of the fuel different fatty acid derivatives can be produced and used. For example, for automobile fuel that is intended to be used in cold climates a branched fatty acid derivative may be desirable and using the teachings provided herein, branched hydrocarbons, fatty acid esters, and alcohols can be made. Using the methods described herein fuels comprising relatively homogeneous fatty acid derivatives that have desired fuel qualities can be produced. Such fuels can be characterized by carbon fingerprinting, their lack of impurities when compared to petroleum derived fuels or bio-diesel derived from triglycerides and, moreover, the fatty acid derivative based fuels can be combined with other fuels or fuel additives to produce fuels having desired properties.
A. Carbon Fingerprinting
Biologically produced fatty acid derivatives represent a new feedstock for fuels, such as alcohols, diesel and gasoline. Some biofuels made using fatty acid derivatives have not been produced from renewable sources and as such, are new compositions of matter. These new fuels can be distinguished from fuels derived form petrochemical carbon on the basis of dual carbon-isotopic fingerprinting. Additionally, the specific source of biosourced carbon (e.g. glucose vs. glycerol) can be determined by dual carbon-isotopic fingerprinting (see, U.S. Pat. No. 7,169,588, which is herein incorporated by reference).
This method usefully distinguishes chemically-identical materials, and apportions carbon in products by source (and possibly year) of growth of the biospheric (plant) component. The isotopes, 14C and 13C, bring complementary information to this problem. The radiocarbon dating isotope (14C), with its nuclear half life of 5730 years, clearly allows one to apportion specimen carbon between fossil (“dead”) and biospheric (“alive”) feedstocks [Currie, L. A. “Source Apportionment of Atmospheric Particles,” Characterization of Environmental Particles, J. Buffle and H. P. van Leeuwen, Eds., 1 of Vol. I of the IUPAC Environmental Analytical Chemistry Series (Lewis Publishers, Inc) (1992) 3 74]. The basic assumption in radiocarbon dating is that the constancy of 14C concentration in the atmosphere leads to the constancy of 14C in living organisms. When dealing with an isolated sample, the age of a sample can be deduced approximately by the relationship t=(−5730/0.693)1n(A/A.sub.O) (Equation 5) where t=age, 5730 years is the half-life of radiocarbon, and A and A.sub.O are the specific 14C activity of the sample and of the modern standard, respectively [Hsieh, Y., Soil Sci. Soc. Am J., 56, 460, (1992)]. However, because of atmospheric nuclear testing since 1950 and the burning of fossil fuel since 1850, 14C has acquired a second, geochemical time characteristic. Its concentration in atmospheric CO2--and hence in the living biosphere--approximately doubled at the peak of nuclear testing, in the mid-1960s. It has since been gradually returning to the steady-state cosmogenic (atmospheric) baseline isotope rate (14C/12C) of ca. 1.2×1012, with an approximate relaxation “half-life” of 7-10 years. (This latter half-life must not be taken literally; rather, one must use the detailed atmospheric nuclear input/decay function to trace the variation of atmospheric and biospheric 14C since the onset of the nuclear age.) It is this latter biospheric 14C time characteristic that holds out the promise of annual dating of recent biospheric carbon. 14C can be measured by accelerator mass spectrometry (AMS), with results given in units of “fraction of modern carbon” (fM). fM is defined by National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) 4990B and 4990C, known as oxalic acids standards HOxI and HOxII, respectively. The fundamental definition relates to 0.95 times the 14C/12C isotope ratio HOxI (referenced to AD 1950). This is roughly equivalent to decay-corrected pre-Industrial Revolution wood. For the current living biosphere (plant material), fM approx 1.1.
The stable carbon isotope ratio (13C /12C) provides a complementary route to source discrimination and apportionment. The 13C /12C ratio in a given biosourced material is a consequence of the 13C /12C ratio in atmospheric carbon dioxide at the time the carbon dioxide is fixed and also reflects the precise metabolic pathway. Regional variations also occur. Petroleum, C3 plants (the broadleaf), C.sub.4 plants (the grasses), and marine carbonates all show significant differences in 13C /12C and the corresponding delta13C values. Furthermore, lipid matter of C3 and C4 plants analyze differently than materials derived from the carbohydrate components of the same plants as a consequence of the metabolic pathway. Within the precision of measurement, 13C shows large variations due to isotopic fractionation effects, the most significant of which for the instant invention is the photosynthetic mechanism. The major cause of differences in the carbon isotope ratio in plants is closely associated with differences in the pathway of photosynthetic carbon metabolism in the plants, particularly the reaction occurring during the primary carboxylation, i.e., the initial fixation of atmospheric CO2. Two large classes of vegetation are those that incorporate the “C3” (or Calvin-Benson) photosynthetic cycle and those that incorporate the “C4” (or Hatch-Slack) photosynthetic cycle. C3 plants, such as hardwoods and conifers, are dominant in the temperate climate zones. In C3 plants, the primary CO2 fixation or carboxylation reaction involves the enzyme ribulose-1,5-diphosphate carboxylase and the first stable product is a 3-carbon compound. C4 plants, on the other hand, include such plants as tropical grasses, corn and sugar cane. In C4 plants, an additional carboxylation reaction involving another enzyme, phosphoenol-pyruvate carboxylase, is the primary carboxylation reaction. The first stable carbon compound is a 4-carbon acid which is subsequently decarboxylated. The CO2 thus released is refixed by the C3 cycle.
Both C4 and C3 plants exhibit a range of 13C /12C isotopic ratios, but typical values are ca. −10 to −14 per mil (C4) and −21 to −26 per mil (C3) [Weber et al., J. Agric. Food Chem., 45, 2942 (1997)]. Coal and petroleum fall generally in this latter range. The 13C measurement scale was originally defined by a zero set by pee dee belemnite (PDB) limestone, where values are given in parts per thousand deviations from this material. The “Δ13C ”, values are in parts per thousand (per mil), abbreviated %, and are calculated as follows:
Since the PDB reference material (RM) has been exhausted, a series of alternative RMs have been developed in cooperation with the IAEA, USGS, NIST, and other selected international isotope laboratories. Notations for the per mil deviations from PDB is Δ13C. Measurements are made on CO2 by high precision stable ratio mass spectrometry (IRMS) on molecular ions of masses 44, 45 and 46.
The fatty acid derivatives and the associated biofuels, chemicals, and mixtures may be completely distinguished from their petrochemical derived counterparts on the basis of 14C (fM) and dual carbon-isotopic fingerprinting, indicating new compositions of matter.
The fatty acid derivatives described herein have utility in the production of biofuels and chemicals. The new fatty acid derivative based product compositions provided by the instant invention additionally may be distinguished on the basis of dual carbon-isotopic fingerprinting from those materials derived solely from petrochemical sources. The ability to distinguish these products is beneficial in tracking these materials in commerce. For example, fuels or chemicals comprising both “new” and “old” carbon isotope profiles may be distinguished from fuels and chemicals made only of “old” materials. Hence, the instant materials may be followed in commerce on the basis of their unique profile and for the purposes of defining competition, and for determining shelf life.
In some examples a biofuel composition is made that includes a fatty acid derivative having δ13C of from about −10.9 to about −15.4, wherein the fatty acid derivative accounts for at least about 85% of biosourced material (derived from a renewable resource such as cellulosic materials and sugars) in the composition. In other examples, the biofuel composition includes a fatty acid derivative having the formula
X-(CH(R))nCH3
wherein X represents CH3, —CH2OR1; —C(O)OR2; or —C(O)NR3R4;
R is, for each n, independently absent, H or lower aliphatic;
n is an integer from 8 to 34, such as from 10 to 24; and
R1, R2, R3 and R4 independently are selected from H and lower alkyl. Typically, when R is lower aliphatic, R represents a branched, unbranched or cyclic lower alkyl or lower alkenyl moiety. Exemplary R groups include, without limitation, methyl, isopropyl, isobutyl, sec-butyl, cyclopentenyl and the like. The fatty acid derivative is additionally characterized as having a δ13C of from about −10.9 to about −15.4; and the fatty acid derivative accounts for at least about 85% of biosourced material in the composition. In some examples the fatty acid derivative in the biofuel composition is characterized by having a fraction of modern carbon (fM 14C) of at least about 1.003, 1.010, or 1.5.
B. Fatty Acid Derivatives
The centane number (CN), viscosity, melting point, and heat of combustion for various fatty acid esters have been characterized in for example, Knothe, Fuel Processing Technology 86:1059-1070, 2005, which is herein incorporated by reference. Using the teachings provided herein a production host can be engineered to produce anyone of the fatty acid esters described in the Knothe, Fuel Processing Technology 86:1059-1070, 2005.
Alcohols (short chain, long chain, branched or unsaturated) can be produced by the production hosts described herein. Such alcohols can be used as fuels directly or they can be used to create an ester, i.e. the A side of an ester as described above. Such ester alone or in combination with the other fatty acid derivatives described herein are useful a fuels.
Similarly, hydrocarbons produced from the microorganisms described herein can be used as biofuels. Such hydrocarbon based fuels can be designed to contain branch points, defined degrees of saturation, and specific carbon lengths. When used as biofuels alone or in combination with other fatty acid derivatives the hydrocarbons can be additionally combined with additives or other traditional fuels (alcohols, diesel derived from triglycerides, and petroleum based fuels).
C. Impurities
The fatty acid derivatives described herein are useful for making bio-fuels. These fatty acid derivatives are made directly from fatty acids and not from the chemical processing of triglycerides. Accordingly, fuels comprising the disclosed fatty acid derivatives will contain less of the impurities than are normally associated with bio-fuels derived from triglycerides, such as fuels derived from vegetable oils and fats.
The crude fatty acid derivative bio-fuels described herein (prior to mixing the fatty acid derivative with other fuels such as traditional fuels) will contain less transesterification catalyst than petrochemical diesel or bio-diesel. For example, the fatty acid derivative can contain less than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% of a transesterification catalyst or an impurity resulting from a transesterification catalyst. Transesterification catalysts include for example, hydroxide catalysts such as NaOH, KOH, LiOH, and acidic catalysts, such as mineral acid catalysts and Lewis acid catalysts. Catalysts and impurities resulting from transesterification catalysts include, without limitation, tin, lead, mercury, cadmium, zinc, titanium, zirconium, hafnium, boron, aluminum, phosphorus, arsenic, antimony, bismuth, calcium, magnesium, strontium, uranium, potassium, sodium, lithium, and combinations thereof.
Similarly, the crude fatty acid derivative bio-fuels described herein (prior to mixing the fatty acid derivative with other fuels such as petrochemical diesel or bio-diesel) will contain less glycerol (or glycerin) than bio-fuels made from triglycerides. For example, the fatty acid derivative can containless than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% glycerol.
The crude biofuel derived from fatty acid derivatives will also contain less free alcohol (i.e. alcohol that is used to create the ester) than bio-diesel made from triglycerides. This is in-part due to the efficiency of utilization of the alcohol by the production host. For example, the fatty acid derivative will contain less than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% free alcohol.
Biofuel derived from the disclosed fatty acid derivatives can be additionally characterized by its low concentration of sulfur compared to petroleum derived diesel. For example, biofuel derived from fatty acid derivatives can have less than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% sulfur.
D. Additives
Fuel additives are used to enhance the performance of a fuel or engine. For example, fuel additives can be used to alter the freezing/gelling point, cloud point, lubricity, viscosity, oxidative stability, ignition quality, octane level, and flash point. In the United States, all fuel additives must be registered with Environmental Protection Agency and companies that sell the fuel additive and the name of the fuel additive are publicly available on the agency website and also by contacting the agency. One of ordinary skill in the art will appreciate that the fatty acid derivatives described herein can be mixed with one or more such additives to impart a desired quality.
One of ordinary skill in the art will also appreciate that the fatty acid derivatives described herein are can be mixed with other fuels such as bio-diesel derived from triglycerides, various alcohols such as ethanol and butanol, and petroleum derived products such as gasoline. In some examples, a fatty acid derivative, such as C16:1 ethyl ester or C18:1 ethyl ester, is produced which has a low gel point. This low gel point fatty acid derivative is mixed with bio-diesel made from triglycerides to lessen the overall gelling point of the fuel. Similarly, a fatty acid derivative such as C16:1 ethyl ester or C18:1 ethyl ester can be mixed with petroleum derived diesel to provide a mixture that is at least and often greater than 5% biodiesel. In some examples, the mixture includes at least 20% or greater of the fatty acid derivative.
For example, a biofuel composition can be made that includes at least about 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90% or 95% of a fatty acid derivative that includes a carbon chain that is 8:0, 10:0, 12:0, 14:0, 14:1, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3, 20:0, 20:1, 20:2, 20:3, 22:0, 22:1 or 22:3. Such biofuel compositions can additionally include at least one additive selected from a cloud point lowering additive that can lower the cloud point to less than about 5° C., or 0° C., a surfactant, or a microemulsion, at least about 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, 85%, 90%, or 95% diesel fuel from triglycerides, petroleum derived gasoline or diesel fuel from petroleum.
EXAMPLESAn exemplary production host is LS9001. LS9001 was produced by modifying C41(DE3) from Overexpress.com (Saint Beausine, France) to functionally deleting the fadE gene (acyl-CoA dehydrogenase).
Briefly, the fadE knock-out strain of E. coli was made using primers YafV_NotI and Ivry_Ol to amplify about 830 by upstream of fadE and primers Lpcaf_ol and LpcaR_Bam to amplify about 960 by downstream of fadE. Overlap PCR was used to create a construct for in frame deletion of the complete fadE gene. The fadE deletion construct was cloned into the temperature sensitive plasmid pKOV3, which contained a SacB gene for counterselection, and a chromosomal deletion of fadE was made according to the method of Link et al., J. Bact. 179:6228-6237, 1997. The resulting strain was not capable of degrading fatty acids and fatty acyl-CoAs (this functional deletion is herein designated as ΔfadE).
Additional modifications that can be included in a production host include introducing a plasmid carrying the four genes which are responsible for acetyl-CoA carboxylase activity in E. coli (accA, B, C, and D, Accessions: NP—414727, NP—417721, NP—417722, NP—416819, EC 6.4.1.2). The accABCD genes were cloned in two steps as bicistronic operons into the NcoI/HindIII and NdeI/AvrII sites of pACYCDuct-1 (Novagen, Madison, Wis.) the resulting plasmid was termed pAS004.126.
Additional modifications that can be included in a production host include the following: over-expression of aceEF (encoding the E1p dehydrogase component and the E2p dihydrolipoamide acyltransferase component of the pyruvate and 2-oxoglutarate dehydrogenase complexes); and fabH/fabD/fabG/acpP/fabF (encoding FAS) from any organism known in the art to encode such proteins, including for example E. coli, Nitrosomonas europaea (ATCC 19718), Bacillus subtilis, Saccharomyces cerevisiae, Streptomyces spp, Ralstonia, Rhodococcus, Corynebacteria, Brevibacteria, Mycobacteria, oleaginous yeast, and the like can be expressed in the production host. Similarly, production hosts can be engineered to express accABCD (encoding acetyl co-A carboxylase) from Pisum savitum instead of, or in addition to, the E. coli homologues. However, when the production host is also producing butanol it is less desirable to express the Pisum savitum homologue.
In some exemplary production hosts, genes can be knocked out or attenuated using the method of Link, et al., J. Bacteriol. 179:6228-6237, 1997. For example, genes that can be knocked out or attenuated include gpsA (encoding biosynthetic sn-glycerol 3-phosphate dehydrogenase, accession NP—418065, EC: 1.1.1.94); ldhA (encoding lactate dehydrogenase, accession NP—415898, EC: 1.1.1.28); pflb (encoding formate acetyltransferase 1, accessions: P09373, EC: 2.3.1.54); adhE (encoding alcohol dehydrogenase, accessions: CAA47743, EC: 1.1.1.1, 1.2.1.10); pta (encoding phosphotransacetylase, accessions: NP—416800, EC: 2.3.1.8); poxB (encoding pyruvate oxidase, accessions: NP—415392, EC: 1.2.2.2); ackA (encoding acetate kinase, accessions: NP—416799, EC: 2:7.2.1) and combinations thereof.
Similarly, the PlsB[D311E] mutation can be introduced into LS9001 to attenuate PlsB using the method described above for the fadE deletion. Once introduced, this mutation will decrease the amount of carbon being diverted to phospholipid production (see,
The following plasmids were constructed for the expression of various proteins that are used in the synthesis of fatty acid derivatives. The constructs were made using standard molecular biology methods and all the cloned genes were put under the control of IPTG-inducible promoters (T7, tac or lac promoters).
The ‘tesA gene (thioesterase A gene accession NP—415027 without leader sequence (Cho and Cronan, J. Biol. Chem., 270:4216-9, 1995, EC: 3.1.1.5, 3.1.2.-) of E. coli was cloned into NdeI/AvrII digested pETDuct-1 (pETDuct-1 described herein is available from Novagen, Madison, Wis.). Genes encoding for FatB-type plant thioesterases (TEs) from Umbellularia California, Cuphea hookeriana and Cinnamonum camphorum (accessions: UcFatB1=AAA34215, ChFatB2=AAC49269, ChFatB3=AAC72881, CcFatB=AAC49151 were individually cloned into three different vectors: (i) NdeI/AvrII digested pETDuet-1, (ii) XhoI/HindIII digested pBluescript KS+ (Stratagene, La Jolla, Calif.)(used to create N-terminal lacZ::TE fusion proteins) and (iii) XbaI/HindIII digested pMAL-c2X (New England Lab, Ipswich, Mass.) (used to create n-terminal MalE::TE fusions). The fadD gene (encoding acyl-CoA synthetase) from E. coli was cloned into a NcoI/HindIII digested pCDFDuet-1 derivative, which contained the acrl gene (acyl-CoA reductase) from Acinetobacter baylyi ADP1 within its NdeI/AvrII sites. Table 7 provides a summary of the plasmids generated to make several exemplary production strains, one of ordinary skill in the art will appreciate that different plasmids and genomic modifications can be used to achieve similar strains
The chosen expression plasmids contain compatible replicons and antibiotic resistance markers, so that a four-plasmid expression system can be established. Therefore, LS9001 can be co-transformed with (i) any of the TE-expressing plasmids, (ii) the FadD-expressing plasmid, which also expresses acrl and (iii) wax synthase expression plasmid. When induced with IPTG, the resulting strain will produce increased concentrations of fatty-alcohols from carbon sources such as glucose. The carbon chain length and degree of saturation of the fatty alcohol produced is dependent on the thioesterase gene that is expressed.
Example 3 Production of Fatty Alcohol in the Recombinant E. coli StrainFatty alcohols were produced by expressing a thioesterase gene and an acyl-CoA reductase gene (FAR) exogenously in a production host. More specifically, plasmids pCDFDuet-1-fadD-acrl (acyl-CoA reductase) and pETDuet-1-‘tesA (thioesterase) were transformed into E. coli strain LS9001 (described in Example 1) and corresponding transformants were selected in LB plate supplemented with 100 mg/L of spectinomycin and 50 mg/L of carbenicillin. Four transformants of LS9001/pCDFDuet-1-fadD-acrl were independently inoculated into 3 mL of M9 medium supplemented with 50 mg/L of carbenicillin and 100 mg/L of spectinomycin). The samples containing the transformants were grown in at 25° C. in a shaker (250 rpm) until they reached 0.5 OD600. 1.5 mL of each sample was transferred into a 250 mL flask containing 30 mL of the medium described above. The resulting culture was grown at 25° C. in a shaker until the culture reached between 0.5-1.0 OD600. IPTG was then added to a final concentration of 1 mM, and growth continued for 40 hours.
The cells were then spun down at 4000 rpm and the cell pellets were suspended in 1.0 mL of methanol. 3 mL of ethyl acetate was then mixed with the suspended cells. 3 mL of H2O were then added to the mixture and the mixture was sonicated for 20 minutes. The resulting sample was centrifuged at 4000 rpm for 5 minutes and the organic phase (the upper phase) which contained fatty alcohol and was subjected to GC/MS analysis. Total alcohol (including tetradecanol, hexadecanol, hexadecenol and octadecenol) yield was about 1-10 mg/L. When an E. coli strain carrying only empty vectors was cultured in the same way, only 0.2-0.5 mg/L of fatty alcohols were found in the ethyl acetate extract.
Example 4 Production and Release of Fatty Alcohol from Production HostAcrl (acyl-CoA reductase) was expressed in E. coli grown on glucose as the sole carbon and energy source. The E. coli produced small amounts of fatty alcohols such as dodecanol (C12:0-OH), tetradecanol (C14:0-OH) and hexadecanol (C16:0-OH). In other samples, FadD (acyl-CoA synthetase) was expressed together with acrl in E. coli and a five-fold increase in fatty alcohol production was observed.
In other samples, acrl, fadD, accABCD (acetyl-CoA Carboxylase) (plasmid carrying accABCD constructed as described in Example 1) were expressed along with various individual thioesterases (TEs) in wildtype E. coli C41(DE3) and an E. coli C41(DE3 ΔfadE, a strain lacking acyl-CoA dehydrogenase. This resulted in additional increases in fatty alcohol production and modulating the profiles of fatty alcohols (see
Expression of ChFatB3 and UcFatB 1 also led to the production of significant amounts of the unsaturated fatty alcohols C16:1-OH and C14:1-OH, respectively. The presence of fatty alcohols was also found in the supernatant of samples generated from the expression of tesA (
Alcohol acetyl transferases (AATs, EC 2.3.1.84), which is responsible for acyl acetate production in various plants, can be used to produce medium chain length waxes, such as octyl octanoate, decyl octanoate, decyl decanoate, and the like. Fatty esters, synthesized from medium chain alcohol (such as C6, C8) and medium chain acyl-CoA (or fatty acids, such as C6 or C8) have a relative low melting point. For example, hexyl hexanoate has a melting point of −55° C. and octyl octanoate has a melting point of −18 to −17° C. The low melting points of these compounds makes them good candidates for use as biofuels.
In this example, a SAAT gene was co-expressed in a production host C41(DE3, ΔfadE) with fadD from E. coli and acrl (alcohol reductase from A. baylyi ADP1) and octanoic acid was provided in the fermentation broth. This resulted in the production of octyl octanoate. Similarly, when the wax synthase gene from A. baylyi ADP1 was expressed in the production host instead of the SAAT gene octyl octanoate was produced.
A recombinant SAAT gene was synthesized using DNA 2.0 (Menlo Park, Calif. 94025). The synthesized DNA was based on the published gene sequence (accession number AF193789) and modified to eliminate the NcoI site. The synthesized SAAT gene (as a BamHI-HindIII fragment) was cloned in pRSET B (Invitrogen, Calsbad, Calif.), linearized with BamHI and HindIII. The resulted plasmid, pHZ1.63A was cotransformed into an E. coli production host with pAS004.114B, which carries a fadD gene from E. coli and acrl gene from A. baylyi ADP1. The transformants were grown in 3 mL of M9 medium with 2% of glucose. After IPTG induction and the addition of 0.02% of octanoic acid, the culture was continued at 25° C. from 40 hours. After that, 3 mL of acetyl acetate was added to the whole culture and mixed several times with mixer. The acetyl acetate phase was analyzed by GC/MS.
Surprising, in the acetyl acetate extract, there is no acyl acetate found. However, a new compound was found and the compound was octyl octanoate. Whereas the control strain without the SAAT gene [C41(DE3, ΔfadE)/pRSET B+pAS004.114B] did not produce octyl octanoate. Also the strain [C41(DE3, ΔfadE)/pHZ1.43 B+pAS004.114B], in which the wax synthase gene from A. baylyi ADP1 was carried by pHZ1.43 produced octyl octanoate (see
The finding that SAAT activity produces octyl octanoate has not reported before and makes it possible to produce medium chain waxes such as octyl octanoate, octyl decanoate, which have low melting point and are good candidates to be use for biofuel to replace triglyceride based biodiesel.
Example 6 Production of Wax Ester in E. coli Strain LS9001Wax esters were produced by engineering an E. coli production host to express a fatty alcohol forming acyl-CoA reductase, thioesterase, and a wax synthase. Thus, the production host produced both the A and the B side of the ester and the structure of both sides was influenced by the expression of the thioesterase gene.
More specifically, wax synthase from A. baylyi ADP1 (termed WSadp1, accessions AA017391, EC: 2.3.175) was amplified with the following primers using genomic DNA from A. baylyi ADP1 as the template. The primers were (1) WSadp1_NdeI, 5′- TCATATGCGCCCATTACATCCG -3′ and (2) WSadp1_Avr, 5′- TCCTAGGAGGGCTAATTTAGCCCTTTAGTT-3′. The PCR product was digested with NdeI and AvrII and cloned into pCOALDeut-1 to give pHZ 1.43. The plasmid carrying WSadp1 was then co-transformed into E. coli strain LS9001 with both pETDuet-1′tesA and pCDFDuet-1-fadD-acrl and transformants were selected in LB plates supplemented with 50 mg/L of kanamycin, 50 mg/L of carbenicillin and 100 mg/L of spectinomycin. Three transformants were inoculated in 3 mL of LBKCS (LB broth supplement with 50 mg/L of kanamycin, 50 mg/L of carbenicillin, 100 mg/L of spectinomycin and 10 g/L of glucose) and cultured at 37° C. shaker (250 rpm). When the cultures reached 0.5 OD600, 1.5 mL of each culture was transferred into 250 mL flasks containing 50 mL of LBKCS and the flasks were grown in a shaker (250 rpm) at 37° C. until the culture reached 0.5-1.0 OD600. IPTG was then added to a final concentration of 1 mM. The induced cultures were grown at 37° C. shaker for another 40-48 hours.
The culture was then placed into 50 mL conical tubes and the cells were spun down at 3500 ×g for 10 minutes. The cell pellet was then mixed with 5 mL of ethyl acetate. The ethyl acetate extract was analyzed with GC/MS. The intracellular yield of waxes (including C16C16, C14:1C16, C18:1C18:1, C2C14, C2C16, C2C16:1, C16C16:1 and C2C18:1) was about 10 mg/L. When an E. coli strain only carrying empty vectors was cultured in the same way, only 0.2 mg/L of wax was found in the ethyl acetate extract.
Example 7 Production and Release of Fatty-Ethyl Ester from Production HostThe LS9001 strain was modified by transforming it with the plasmids carrying a wax synthase gene from A. baylyi (plasmid pHZ1.43), a thioesterase gene from Cuphea hookeriana (plasmid pMAL-c2X-TEcu) and a fadD gene from E. coli (plasmid pCDFDuet-1-fadD). This recombinant strain was grown at 25° C. in 3 mL of M9 medium with 50 mg/L of kanamycin, 100 mg/L of carbenicillin and 100 mg/L of spectinomycin. After IPTG induction, the media was adjusted to a final concentration of 1% ethanol and 2% glucose. The culture was allowed to grow for 40 hours after IPTG induction. The cells were separated from the spent medium by centrifugation at 3500 ×g for 10 minutes). The cell pellet was re-suspended with 3 mL of M9 medium. The cell suspension and the spent medium were then extracted with 1 volume of ethyl acetate. The resulting ethyl acetate phases from the cells suspension and the supernatant were subjected to GC-MS analysis. The results showed that the C16 ethyl ester was the most prominent ester species (as expected for this thioesterase, see Table 1), and that 20% of the fatty acid ester produced was released from the cell (see
The thioesterases FatB3 (C. hookeriana), TesA (E. coli), and FatB (U. california) were expressed simultaneously with wax synthase (A. baylyi). A plasmid termed pHZ1.61 was constructed by replacing the NotI/AvrII fragment (carrying the acrl gene) with the NotI-AvrII fragment from pHZ1.43 so that fadD and the ADP1 wax synthase were in one plasmid and both coding sequences were under the control of separate T7 promoter. The construction of pHZ1.61 made it possible to use a two plasmid system instead of the three plasmid system as described in Example 6. pHZ1.61 was then co-transformed into E. coli C41(DE3, ΔfadE) with one of the various plasmids carrying the different thioesterase genes stated above.
The total fatty acid ethyl esters (supernatant and intracellular fatty acid ethyl esters) produced by these transformants were evaluated using the technique described herein. The yields and the composition of fatty acid ethyl esters are summarized in Table 8.
The genes that control fatty acid production are conserved between microorganisms. For example, Table 9 identifies the homologues of many of the genes described herein which are known to be expressed in microorganisms that produce hydrocarbons. To increase fatty acid production and, therefore, hydrocarbon production in microorganisms such as those identified in Table 9, heterologous genes, such as those from E. coli can be expressed. One of ordinary skill in the art will also appreciate that genes that are endogenous to the micoorganisms provided in Table 9 can also be over-expressed, or attenuated using the methods described herein. Moreover, genes that are described in
For example, exogenous nucleic acid sequences encoding acetyl-CoA carboxylase are introduced into K. radiotolerans. The following genes comprise the acetyl-CoA carboxylase protein product in K. radiotolerans; acetyl CoA carboxylase, alpha subunit (accA/ZP—00618306), acetyl-CoA carboxylase, biotin carboxyl carrier protein (accB/ZP—00618387), acetyl-CoA carboxylase, biotin carboxylase subunit (accC/ZP—00618040), and acetyl-CoA carboxylase, beta (carboxyltranferase) subunit (accD/ZP—00618306). These genes are cloned into a plasmid such that they make a synthetic acetyl-CoA carboxylase operon (accABCD) under the control of a K. radiotolerans expression system such as the expression system disclosed in Ruyter et al., Appl Environ Microbiol. 62:3662-3667, 1996. Transformation of the plasmid into K. radiotolerans will enhance fatty acid production. The hydrocarbon producing strain of K. radiotolerans can also be engineered to make branched, unsaturated hydrocarbons having specific carbon chain lengths using the methods disclosed herein.
Table 10, below provides additional exemplary production strains. Two example biosynthetic pathways are described for producing fatty acids, fatty alcohols, and wax esters. A genetically engineered host can be produced by cloning the expression of the accABCD genes from E. coli, the ‘tesA gene from E. coli, and fadD gene from E. coli into a host cell. Host cells can be selected from E. coli, yeast, add to the list. These genes can also be transformed into a host cell that is modified to contain one or more of the genetic manipulations described in Examples 1 and 2, above.
Example 11 FermentationHost microorganisms can be also engineered to express umuC and umuD from E. coli in pBAD24 under the prpBCDE promoter system through de novo synthesis of this gene with the appropriate end-product production genes. For small scale hydrocarbon product production, E. coli BL21(DE3) cells harbouring pBAD24 (with ampicillin resistance and the end-product synthesis pathway) as well as pUMVC1 (with kanamycin resistance and the acetyl CoA/malonyl CoA over-expression system) are incubated overnight at at 37° C. shaken at >200 rpm 2 L flasks in 500 ml LB medium supplemented with 75 μg/mL ampicillin and 50 μg/ml kanamycin until cultures reached an OD600 of >0.8. Upon achieving an OD600 of >0.8, cells are supplemented with 25 mM sodium proprionate (pH 8.0) to activate the engineered gene systems for production as well as to stop cellular proliferation (through activation of umuC and umuD proteins). Induction is performed for 6 hours at 30° C. After incubation, media is examined for product using GC- MS (as described below).
For large scale product production, the engineered microorganisms are grown in 10 L, 100 L or larger batches, fermented and induced to express desired products based on the specific genes encoded in plasmids as appropriate. E. coli BL21(DE3) cells harbouring pBAD24 (with ampicillin resistance and the end-product synthesis pathway) as well as pUMVC1 (with kanamycin resistance and the acetyl-CoA/malonyl-CoA over-expression system) are incubated from a 500 mL seed culture for 10 L fermentations (5 L for 100 L fermentations) in LB media (glycerol free) at 37° C. shaken at >200 rpm until cultures reached an OD600 of >0.8 (typically 16 hours) incubated with 50 □g/mL kanamycin and 75 μg/mL ampicillin. Media is treated with continuously supplemented to maintain a 25 mM sodium proprionate (pH 8.0) to activate the engineered in gene systems for production as well as to stop cellular proliferation (through activation of umuC and umuD proteins). Media is continuously supplemented with glucose to maintain a concentration 90 g/100 mL. After the first hour of induction, aliquots of no more than 10% of the total cell volume are removed each hour and allowed to sit unaggitated so as to allow the hydrocarbon product to rise to the surface and undergo a spontaneous phase separation. The hydrocarbon component is then collected and the aqueous phase returned to the reaction chamber. The reaction chamber is operated continuously. When the OD.sub.600 drops below 0.6, the cells are replaced with a new batch grown from a seed culture.
For wax ester production, subsequent to isolation, the wax esters are washed briefly in 1 M HCl to split the ester bond, and returned to pH 7 with extensive washing with distilled water.
Example 12 Product CharacterizationTo characterize and quantify the fatty alcohols and fatty acid esters, gas chromatography (GC) coupled with electron impact mass spectra (MS) detection was used. Fatty alcohol samples were first derivatized with an excess of N-trimethylsilyl (TMS) imidazole to increase detection sensitivity. Fatty acid esters did not required derivatization. Both fatty alcohol-TMS derivatives and fatty acid esters were dissolved in an appropriate volatile solvent, like ethyl acetate. The samples were analyzed on a 30 m DP-5 capillary column using the following method. After a 14 splitless injection onto the GC/MS column, the oven is held at 100° C. for 3 minutes. The temperature was ramped up to 320° C. at a rate of 20° C./minute. The oven was held at 320° C. for an additional 5 minutes. The flow rate of the carrier gas helium was 1.3 mL/minute. The MS quadrapole scans from 50 to 550 m/z. Retention times and fragmentation patterns of product peaks were compared with authentic references to confirm peak identity.
For example, hexadeconic acid ethyl ester eluted at 10.18 minutes (
Quantification was carried out by injecting various concentrations of the appropriate authentic references using the GC/MS method described above. This information was used to generate a standard curve with response (total integrated ion count) versus concentration.
EquivalentsWhile specific examples of the subject inventions are explicitly disclosed herein, the above specification and examples herein are illustrative and not restrictive. Many variations of the inventions will become apparent to those skilled in the art upon review of this specification including the examples. The full scope of the inventions should be determined by reference to the examples, along with their full scope of equivalents, and the specification, along with such variations.
Claims
1. A method of producing a fatty alcohol composition in a recombinant microorganism, comprising the steps of:
- (a) genetically engineering a microorganism to comprise a nucleic acid sequence encoding a polypeptide having acetyl-CoA carboxylase activity (EC 6.4.1.2), and a nucleic acid sequence encoding a polypeptide having fatty alcohol forming activity, resulting in a recombinant microorganism;
- (b) culturing the recombinant microorganism in a culture medium containing a carbon source under conditions effective to overexpress the acetyl-CoA carboxylase polypeptide and the polypeptide having fatty alcohol forming activity, wherein a fatty alcohol composition is produced by said cultured recombinant microorganism; and
- (c) optionally recovering the fatty alcohol composition from the cell culture.
2. The method of claim 1, further comprising genetically engineering said microorganism to comprise at least one nucleic acid sequence encoding a polypeptide having thioesterase activity, wherein said thioesterase polypeptide is expressed.
3. The method of claim 1, wherein said polypeptide having fatty alcohol forming activity is (i) a fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), or (ii) an acyl-CoA reductase (EC 1.2.1.50) and an alcohol dehydrogenase (EC 1.1.1.1).
4. The method of claim 2, wherein said polypeptide having fatty alcohol forming activity is (i) a fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), or (ii) an acyl-CoA reductase (EC 1.2.1.50) and an alcohol dehydrogenase (EC 1.1.1.1).
5. The method of claim 4, wherein said polypeptide having fatty alcohol forming activity is a fatty alcohol forming acyl-CoA reductase.
6. The method of claim 1, wherein said the fatty alcohol composition comprises one or more of saturated or unsaturated C12, C14 or C16 fatty alcohols.
7. A recombinant microorganism comprising:
- (a) a nucleic acid sequence encoding a branched chain alpha-keto acid dehydrogenase 60 (Bkd) operon including branched-chain α-keto acid decarboxylase α and β subunits (E1α/β), a dihydrolipoyl transacylase component (E2), and a dihydrolipoyl dehydrogenase component (E3); and
- (b) a nucleic acid sequence encoding a β-ketoacyl-ACP synthase III protein
- (FabH, EC 2.3.1.41) with specificity for a branched chain acyl CoA molecule, wherein at least one nucleic acid sequence according to (a) or (b) is exogenous to the recombinant microorganism and wherein the recombinant microorganism produces a branched fatty acid derivative when cultured in the presence of a carbon source under conditions effective to express the nucleic acid sequences according to (a) and (b).
8. The recombinant microorganism according to claim 7, wherein the nucleic acid sequence encoding the FabH protein with specificity for a branched chain acyl CoA molecule is exogenous to the recombinant microorganism and the expression of a FabH endogenous to the recombinant microorganism and lacking specificity for a branched chain acyl CoA molecule is attenuated.
9. The recombinant microorganism according to claim 7, further comprising a nucleic acid sequence encoding at least one polypeptide having thioesterase activity.
10. The recombinant microorganism according to claim 9, further comprising a nucleic acid sequence encoding a polypeptide having fatty alcohol forming activity.
11. The recombinant microorganism according to claim 10, wherein said polypeptide having fatty alcohol forming activity is (i) a fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), or (II) acyl-CoA reductases (EC 1.2.1.50) and alcohol dehydrogenase (EC 1.1.1.1).
12. The recombinant microorganism according to claim 11, wherein said polypeptide having fatty alcohol forming activity is a fatty alcohol forming acyl-CoA reductase.
13. A recombinant microorganism culture, comprising:
- the recombinant microorganism according to claim 11 and a fermentation medium comprising a carbon source.
14. A branched fatty alcohol composition produced by the recombinant microorganism culture according to claim 13, wherein said fatty alcohol composition comprises one or more of saturated or unsaturated C12, C14 and C16 fatty alcohols.
15. A branched fatty alcohol composition obtained from the supernatant of the recombinant microorganism culture of claim 13 wherein the fatty alcohol composition comprises C12 and C14 fatty alcohols.
16. A branched fatty alcohol composition obtained from the supernatant of the recombinant microorganism culture of claim 13, wherein the fatty alcohol composition comprises unsaturated fatty alcohols.
17. A branched fatty alcohol composition obtained from the supernatant of the recombinant microorganism culture of claim 13, wherein the fatty alcohol composition comprises saturated fatty alcohols.
18. A method of producing a branched fatty alcohol composition in a recombinant microorganism, comprising the steps of:
- (a) obtaining a genetically engineered recombinant microorganism according to claim 11;
- (b) culturing the recombinant microorganism in a culture medium containing a carbon source under conditions effective to express said: (i) Bkd operon; (ii) FabH;
- (iii) a nucleic acid sequence encoding a polypeptide having fatty alcohol forming activity; and (iv) nucleic acid sequence encoding a polypeptide having thioesterase activity; and
- (c) optionally recovering the branched fatty alcohol composition from the cell culture.
19. The method of claim 18, wherein said polypeptide having fatty alcohol forming activity is (i) a fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), or (II) an acyl-CoA reductase (EC 1.2.1.50) and an alcohol dehydrogenase (EC 1.1.1.1).
20. The recombinant microorganism according to claim 19, wherein said polypeptide having fatty alcohol forming activity is a fatty alcohol forming acyl-CoA reductase.
Type: Application
Filed: Nov 22, 2011
Publication Date: Jun 7, 2012
Applicant: LS9, INC. (South San Francisco, CA)
Inventors: Jay D. KEASLING (Berkeley, CA), Zhihao Hu (South San Francisco, CA), Chris Somerville (Berkeley, CA), George Church (Brookline, MA), David Berry (Cambridge, MA), Lisa Friedman (San Francisco, CA), Andreas Schirmer (South San Francisco, CA), Shane Brubaker (El Cerrito, CA), Stephen B. Del Cardayre (South San Francisco, CA)
Application Number: 13/302,957
International Classification: C12P 7/04 (20060101); C12N 1/19 (20060101); C12N 1/21 (20060101); C07C 33/025 (20060101); C07C 31/125 (20060101);
