STEVIOL GLYCOSIDE TRANSPORT
A recombinant host capable of producing a steviol glycoside which overexpresses a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto. A recombinant host capable of producing a steviol glycoside which has been modified, preferably in its genome, to result in a deficiency in the production of a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
The present invention relates to a recombinant host capable of producing a steviol glycoside. The invention also relates to a process for the preparation of a steviol glycoside using such a recombinant host. The invention also relates to a fermentation broth comprising a steviol glycoside, a steviol glycoside and to a composition comprising two or more steviol glycosides. The invention further relates to a foodstuff, feed or beverage which comprises a steviol glycoside or a composition comprising two or more steviol glycosides.
BACKGROUND TO THE INVENTIONThe leaves of the perennial herb, Stevia rebaudiana Bert., accumulate quantities of intensely sweet compounds known as steviol glycosides. Whilst the biological function of these compounds is unclear, they have commercial significance as alternative high potency sweeteners.
These sweet steviol glycosides have functional and sensory properties that appear to be superior to those of many high potency sweeteners. In addition, studies suggest that stevioside can reduce blood glucose levels in Type II diabetics and can reduce blood pressure in mildly hypertensive patients.
Steviol glycosides accumulate in Stevia leaves where they may comprise from 10 to 20% of the leaf dry weight. Stevioside and rebaudioside A are both heat and pH stable and suitable for use in carbonated beverages and many other foods. Stevioside is between 110 and 270 times sweeter than sucrose, rebaudioside A between 150 and 320 times sweeter than sucrose. In addition, rebaudioside D is also a high-potency diterpene glycoside sweetener which accumulates in Stevia leaves. It may be about 200 times sweeter than sucrose. Rebaudioside M is a further high-potency diterpene glycoside sweetener. It is present in trace amounts in certain stevia variety leaves, but has been suggested to have a superior taste profile.
Steviol glycosides have traditionally been extracted from the Stevia plant. In Stevia, (−)-kaurenoic acid, an intermediate in gibberellic acid (GA) biosynthesis, is converted into the tetracyclic diterpene steviol, which then proceeds through a multi-step glycosylation pathway to form the various steviol glycosides. However, yields may be variable and affected by agriculture and environmental conditions. Also, Stevia cultivation requires substantial land area, a long time prior to harvest, intensive labour and additional costs for the extraction and purification of the glycosides.
More recently, interest has grown in producing steviol glycosides using fermentative processes. WO2013/110673 and WO2015/007748 describe microorganisms that may be used to produce at least the steviol glycosides rebaudioside A, rebaudioside D and rebaudioside M.
Further improvement of such microoganisms is desirable in order that higher amounts of steviol glycosides may be produced and/or additional or new steviol glycosides and/or higher amounts of specific steviol glycosides and/or mixtures of steviol glycosides having desired ratios of different steviol glycosides.
SUMMARY OF THE INVENTIONThe present invention is based on the identification of proteins which are capable of mediating steviol glycoside transport.
Accordingly, one or more such proteins may be overexpressed in a recombinant host (such as a microbial cell) in order to increase steviol glycoside transport out of the host. Alternatively, a host (such as a microbial cell) may be modified so as to express less of one or more such proteins than a corresponding non-modified version of the host. In this case, more steviol glycoside may be retained within the host which is then glycosylated to a steviol glycoside comprising a higher number of sugar moieties.
Thus, the invention relates to a recombinant host, for example a cell such as a microbial cell, which produces steviol glycoside outside the host to a greater degree than a corresponding host not overexpressing the protein. This may facilitate easier recovery of steviol glycosides. The invention also relates to a recombinant host capable of producing a steviol glycoside which overexpresses a heterologous polypeptide which mediates steviol glycoside transport.
Accordingly, the invention relates to a recombinant host capable of producing a steviol glycoside which overexpresses a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
The invention also relates to a recombinant host capable of producing a steviol glycoside which has been modified, preferably in its genome, to result in a deficiency in the production of a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 of SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
The invention also relates to a recombinant host which comprises steviol glycosides (inside and/or outside the host) having a higher or lower average glycosylation number than a corresponding host not modified according to the invention.
The invention also relates to:
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- a process for the preparation of a steviol glycoside which comprises fermenting a recombinant host according to any one of the preceding claims in a suitable fermentation medium and, optionally, recovering the steviol glycoside;
- a fermentation broth comprising a steviol glycoside obtainable by a process of the invention;
- a steviol glycoside obtained by a process or a fermentation broth of the invention;
- a composition comprising two or more steviol glycosides of the invention or obtainable by a process of the invention;
- a foodstuff, feed or beverage which comprises a steviol glycoside or a composition of the invention.
A description of the sequences is set out in Table 15. Sequences described herein may be defined with reference to the sequence listing or with reference to the database accession numbers also set out in Table 15.
DETAILED DESCRIPTION OF THE INVENTIONThroughout the present specification and the accompanying claims, the words “comprise”, “include” and “having” and variations such as “comprises”, “comprising”, “includes” and “including” are to be interpreted inclusively. That is, these words are intended to convey the possible inclusion of other elements or integers not specifically recited, where the context allows.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to one or at least one) of the grammatical object of the article. By way of example, “an element” may mean one element or more than one element.
The invention relates to the identification of polypeptides which are capable of mediating steviol glycoside transport. Such a polypeptide may directly mediate steviol glycoside transport, i.e. may be a transporter protein, or may indirectly mediate steviol glycoside transport. Such a polypeptide may be capable of mediating transport of one or more steviol glycoside.
The invention relates to a recombinant host either overexpressing or having reduced expression of such a polypeptide. The terms recombinant host or recombinant cell may, depending on the context, be used interchangeably.
Such a polypeptide as described herein may be overexpressed in a recombinant host, such as a recombinant host cell, capable of producing one or more steviol glycosides. Such a cell may be capable of producing more of one or more steviol glycosides external to the cell than a corresponding cell which does not overexpress the polypeptide. That is to say, a recombinant cell according to the invention may have increased or decreased steviol glycoside transport in a comparison with a corresponding non-recombinant cell.
Accordingly, the invention provides a recombinant host capable of producing a steviol glycoside which overexpresses a polypeptide, the polypeptide being one which is capable of mediating steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
The expression of such a polypeptide may also be modified in a host, such as a recombinant host cell, such that it is reduced compared to a corresponding cell which has not been similarly modified. In this way, the amount of one or more steviol glycosides outside the cell may be reduced in comparison with a corresponding cell which has not been similarly modified. This may allow for increased glycosylation of one or more steviol glycosides within the cell compared with a corresponding cell which has not been similarly modified. Such a host may thus comprise steviol glycosides having a higher average glycosylation number compared with a corresponding cell which has not been similarly modified.
Accordingly, the invention provides a recombinant host capable of producing a steviol glycoside which has been modified, preferably in its genome, to result in a deficiency in the production of a polypeptide, the polypeptide being one which is capable of mediating steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
A host cell of the invention is a recombinant host cell. “Recombinant” in this sense means that the host cell is a non-naturally occurring host cell, for example modified by introduction of one or more nucleic acids using recombinant techniques. A nucleic acid used to modify a host cell to arrive at a recombinant host cell of the invention may be a naturally-occurring nucleic acid or a non-naturally occurring nucleic acid.
Thus, when used in reference to a host of the invention, “recombinant” indicates that a cell has been modified by the introduction of one or more heterologous nucleic acid or protein or the alteration of a native nucleic acid or protein, or that the cell is derived from a cell so modified. The term “heterologous” as used herein refers to nucleic acid or amino acid sequences not naturally occurring in a host cell. In other words, the nucleic acid or amino acid sequence is not identical to that naturally found in the host cell.
The invention relates to a recombinant host capable of producing a steviol glycoside which overexpresses a heterologous polypeptide which mediates steviol glycoside transport. Such a heterologous polypeptide may be obtained from or derived from a genus or species other than that of the host. Accordingly, if the recombinant host is a yeast, the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from a different genus or species of yeast.
For example, if the host cell is a Saccharomyces (e.g., S. cerevisiae, S. bayanus, S. pastorianus, S. carlsbergensis), the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from a Candida (e.g., C. krusei, C. revkaufi, C. pulcherrima, C. tropicalis, C. utilis), an Issatchenkia (eg. I. orientalis) or a Yarrowia (e.g., Y. lipolytica (formerly classified as Candida lipolytica)).
For example, if the host cell is a Candida (e.g., C. krusei, C. revkaufi, C. pulcherrima, C. tropicalis, C. utilis), the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from a Saccharomyces (e.g., S. cerevisiae, S. bayanus, S. pastorianus, S. carlsbergensis), an Issatchenkia (eg. I. orientalis) or a Yarrowia (e.g., Y. lipolytica (formerly classified as Candida lipolytica)).
For example, if the host cell is an Issatchenkia (eg. I. orientalis), the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from a Saccharomyces (e.g., S. cerevisiae, S. bayanus, S. pastorianus, S. carlsbergensis), a Candida (e.g., C. krusei, C. revkaufi, C. pulcherrima, C. tropicalis, C. utilis) or a Yarrowia (e.g., Y. lipolytica (formerly classified as Candida lipolytica)).
For example, if the host cell is a Yarrowia (e.g., Y. lipolytica (formerly classified as Candida lipolytica)), the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from a Saccharomyces (e.g., S. cerevisiae, S. bayanus, S. pastorianus, S. carlsbergensis). a Candida (e.g., C. krusei, C. revkaufi, C. pulcherrima, C. tropicalis, C. utilis) or an Issatchenkia (eg. I. orientalis).
If the host cell is Saccharomyces cerevisiae, the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from Yarrowia lipolytica (formerly classified as Candida lipolytica)), Candida krusei or Issatchenkia orientalis.
If the host cell is Yarrowia lipolytica, the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from Saccharomyces cerevisiae, Yarrowia lipolytica (formerly classified as Candida lipolytica)) or Candida krusei or Issatchenkia orientalis.
If the host cell is Candida krusei or Issatchenkia orientalis, the heterologous polypeptide which mediates steviol glycoside transport may be obtained from or derived from Saccharomyces cerevisiae or Yarrowia lipolytica.
The term “derived from” also includes the terms “originated from,” “obtained from,” “obtainable from,” “isolated from,” and “created from,” and generally indicates that one specified material find its origin in another specified material or has features that can be described with reference to the another specified material. As used herein, a substance (e.g., a nucleic acid molecule or polypeptide) “derived from” a microorganism may indicate that the substance is native to that microorganism or is a substance native to that microorganism, but may also indicate a substance that has been altered from a native version.
Thus, for example, a recombinant cell may express a polypeptide as defined herein not found within the native (non-recombinant) form of the cell. Alternatively, a recombinant cell may be modified so as to express a native gene encoding a polypeptide as defined herein to a greater degree than takes place within the native “non-recombinant” form of the cell.
Alternatively, a recombinant cell may be modified so as to express a native gene encoding a polypeptide as defined herein to a lesser degree than takes place within the native “non-recombinant” form of the cell.
In a cell of the invention, a polypeptide as defined herein may be overexpressed. Herein, “overexpressed”, “overexpression” or the like implies that the recombinant host cell expresses more of the polypeptide than a corresponding cell which does not overexpress the polypeptide or, alternatively, that the polypeptide is expressed in a cell which would not typically express that protein. Alternatively, overexpression may be achieved by expressing a variant polypeptide having a higher specific activity.
A recombinant cell of the invention cell may be modified, preferably in its genome, to result in a deficiency in the production of a polypeptide as defined herein.
Such a cell may be from a parent host cell and be modified, preferably in its genome, if compared to the parent host cell to obtain a different genotype and/or a different phenotype if compared to the parent host cell from which it is derived.
Such a cell which has been modified, preferably in its genome, to result in a deficiency in the production of a polypeptide as defined herein, is a mutant host cell which has been modified, preferably in its genome, to result in a phenotypic feature wherein the cell: a) produces less of the product or produces substantially no product and/or b) produces a product having a decreased activity or decreased specific activity or a product having no activity or no specific activity and combinations of one or more of these possibilities as compared to the parent microbial host cell that has not been modified, when analyzed under the same conditions.
Such a recombinant host may be a full or partial knock-out of a nucleic acid sequence encoding a polypeptide as described herein.
The term “recombinant” is synonymous with “genetically modified”.
The invention thus concerns recombinant hosts overexpressing or deficient in a polypeptide identified as having steviol glycoside transport mediating activity: typically, the host is one which may be used for the production of steviol glycosides. The ability of a given recombinant host to produce a steviol glycoside may be a property of the host in non-recombinant form or may be a result of the introduction of one or more recombinant nucleic acid sequences (i.e. encoding enzymes leading to the production of a steviol glycoside).
For the purpose of this invention, a polypeptide having steviol glycoside transport mediating activity (i.e. a polypeptide which mediates steviol glycoside transport) is one which has an effect on transport of one or more steviol glycosides across a cell membrane. The effect may be direct, i.e. the polypeptide may be a transporter protein or comprise a functional transporter region. Alternatively, the effect may be indirect, i.e. the polypeptide is not a transporter protein, but its activity nevertheless has an effect on steviol glycoside transport.
Typically, the effect will be such that increasing the level of expression of the polypeptide increases the amount of transport of one or more steviol glycosides across the membrane of a cell (in comparison with a corresponding cell having a lower level of expression of the polypeptide). Conversely, decreasing the level of expression of the polypeptide may decrease the amount of transport of one or more steviol glycosides across the membrane of a cell (in comparison with a corresponding cell having a higher level of expression of the polypeptide).
Typically, a recombinant host of the invention is capable of producing a steviol glycoside. For example, a recombinant host of the invention may be capable of producing one or more of, for example but not limited to, steviol-13-monoside, steviol-19-monoside, 13-[(β-D-Glucopyranosyl)oxy)kaur-16-en-18-oic acid 2-O-β-D-glucopyranosyl-β-D-glucopyranosyl ester, rubusoside, stevioside, steviol-19-diside, steviolbioside, rebA, rebB, rebC, rebD, rebE or rebM. A recombinant host of the invention may be capable of producing one or more of the steviol glycosides set out in Ceunen and Geuns, Journal of Natural Products 76(6), 1201-1228, 2013.
Thus, a cell of the invention may be one in which the amount of total amount of steviol glycosides outside the cell as compared with inside the cell is greater or less than compared with a corresponding cell which either does not overexpress or does not have a reduced level of expression of a cell of the invention.
Alternatively, a cell of the invention may have the same total amount of steviol glycosides outside the cell as compared with inside the cell compared with a corresponding cell which either does not overexpress or does not have a reduced level of expression of a cell of the invention, but may have an altered distribution of steviol glycosides inside and outside the cell.
Thus, a recombinant host of the invention is capable of producing a steviol glycoside. For example, a recombinant host of the invention may be capable of producing one or more of, for example, steviol-β-monoside, steviol-19-monoside, 13-[(β-D-Glucopyranosyl)oxy)kaur-16-en-18-oic acid 2-O-β-D-glucopyranosyl-β-D-glucopyranosyl ester, rubusoside, stevioside, steviol-19-diside, steviolbioside, rebA, rebB, rebC, rebD, rebE or rebM.
Thus, a recombinant host of the invention may be one in which at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% of the rebA produced by the cell is outside the cell.
Thus, a recombinant host of the invention may be one in which at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% of the rebD produced by the cell is outside the cell.
Thus, a recombinant host of the invention may be one in which at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50% of the rebM produced by the cell is outside the cell.
A recombinant cell of the invention may be one in which no more than about 50%, no more than about 40%, no more than about 30%, no more than about 20%, no more than about 10% of the rebA produced by the cell is outside the cell.
A recombinant cell of the invention may be one in which no more than about 50%, no more than about 40%, no more than about 30%, no more than about 20%, no more than about 10% of the rebD produced by the cell is outside the cell.
A recombinant cell of the invention may be one in which no more than about 50%, no more than about 40%, no more than about 30%, no more than about 20%, no more than about 10% of the rebM produced by the cell is outside the cell.
A recombinant cell of the invention may be one where the average glycosylation number of the steviol glycosides is at least 3, at least 4, at least 5, at least 6 or more. The average glycosylation number may be increased or decreased in comparison with a corresponding cell not modified according to the invention. For example, average glycosylation may decrease when a polypeptide as described herein is overexpressed. For example, average glycosylation may increase (in particular in a cell itself) when expression of a polypeptide of the invention is reduced.
The average glycosylation may refer to that in the supernatant of a recombinant cell of the invention or to the average glycosylation in the broth (pellet+supernatant).
The invention thus provides a recombinant cell capable of producing a steviol glycoside either overexpressing or deficient in the expression of a polypeptide comprising the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto. Such an amino acid sequence has an effect of steviol glycoside transport, i.e. is a mediator of steviol glycoside transport.
The polypeptide may also be defined as one comprising the following amino acid sequence (or an amino acid sequence having at least about 45% sequence identity thereto):
A polypeptide, typically having steviol glycoside transport mediating activity, may comprise an amino acid sequence having at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about, 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98% or at least about 99% sequence identity to SEQ ID NO: 35.
A polypeptide, typically having steviol glycoside transport mediating activity, may comprise an amino acid sequence having at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about, 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98% or at least about 99% sequence identity to SEQ ID NO: 38.
A polypeptide, typically having steviol glycoside transport mediating activity, encoded by a recombinant nucleic acid present in a recombinant host of the invention may comprise an amino acid sequence which is a fragment of an amino acid sequence described herein, for example a truncated version of such an amino acid sequence.
That is to say, the invention also a recombinant host overexpressing a biologically active fragment of a polypeptide having steviol glycoside transport mediating activity as described herein.
Biologically active fragments of a polypeptide of the invention include polypeptides comprising amino acid sequences sufficiently identical to or derived from the amino acid sequence of SEQ ID NO: 29 which include fewer amino acids than the full-length polypeptide as given in SEQ ID NO: 29, but which exhibit at least one biological activity of the corresponding full-length polypeptide.
Typically, biologically active fragments comprise a domain or motif with at least one activity of the polypeptide of the invention. A biologically active fragment of a polypeptide of the invention can be a polypeptide which is, for example, about 10, about 25, about 50, about 100 or more amino acids in length or at least about 100 amino acids, at least 150, 200, 250, 300, 350, 400, 600, 1000 amino acids in length, or of a length up to the total number of amino acids of the polypeptide of the invention. Moreover, other biologically active portions, in which other regions of the polypeptide are deleted, can be prepared by recombinant techniques and evaluated for one or more of the biological activities of the native form of a polypeptide of the invention. The invention also features nucleic acid fragments which encode the above biologically active fragments of the polypeptide of the invention.
A recombinant host of the invention may overexpress or be deficient in such a polypeptide.
A recombinant host of the invention may comprise recombinant nucleic acid sequences encoding more than one such polypeptide, for example two, three, four or more such polypeptides. The polypeptides thus encoded may be the same or different.
A recombinant cell of the invention may be modified so as to reduce the expression level of more than one such polypeptide, for example two, three, four or more such polypeptides.
An overexpressed polypeptide encoded by a recombinant nucleic acid present in a recombinant host may be one which is obtainable from or derived from or found in an organism of the genus Pichia, for example one which is obtainable from or derived from or found in a Pichia kudriavzeii.
As used herein, the term “polypeptide” refers to a molecule comprising amino acid residues linked by peptide bonds and containing more than five amino acid residues. The amino acids are identified by either the single-letter or three-letter designations. The term “protein” as used herein is synonymous with the term “polypeptide” and may also refer to two or more polypeptides. Thus, the terms “protein”, “peptide” and “polypeptide” can be used interchangeably. Polypeptides may optionally be modified (e.g., glycosylated, phosphorylated, acylated, farnesylated, prenylated, sulfonated, and the like) to add functionality. Polypeptides exhibiting activity may be referred to as enzymes. It will be understood that, as a result of the degeneracy of the genetic code, a multitude of nucleotide sequences encoding a given polypeptide may be produced.
A polypeptide encoded by a recombinant nucleic acid for use in a recombinant host of the invention may comprise a signal peptide and/or a propeptide sequence. In the event that a polypeptide of the invention comprises a signal peptide and/or a propeptide, sequence identity may be calculated over the mature polypeptide sequence.
A recombinant nucleic acid sequence for use in a recombinant host of the invention may be provided in the form of a nucleic acid construct. The term “nucleic acid construct” refers to a nucleic acid molecule, either single- or double-stranded, which is isolated from a naturally occurring gene or which has been modified to contain segments of nucleic acid which are combined and juxtaposed in a manner which would not otherwise exist in nature. The term nucleic acid construct is synonymous with the term “expression cassette” when the nucleic acid construct contains all the control sequences required for expression of a coding sequence, wherein said control sequences are operably linked to said coding sequence.
A recombinant nucleic acid sequence for use in a recombinant host of the invention may be provided in the form of an expression vector, wherein the polynucleotide sequence is operably linked to at least one control sequence for the expression of the polynucleotide sequence in a recombinant host cell.
The term “operably linked” as used herein refers to two or more nucleic acid sequence elements that are physically linked and are in a functional relationship with each other. For instance, a promoter is operably linked to a coding sequence if the promoter is able to initiate or regulate the transcription or expression of a coding sequence, in which case the coding sequence should be understood as being “under the control of” the promoter. Generally, when two nucleic acid sequences are operably linked, they will be in the same orientation and usually also in the same reading frame. They usually will be essentially contiguous, although this may not be required.
An expression vector comprises a polynucleotide coding for a polypeptide as described herein, operably linked to the appropriate control sequences (such as a promoter, and transcriptional and translational stop signals) for expression and/or translation in vitro, or in the host cell of the polynucleotide.
The expression vector may be any vector (e.g., a plasmid or virus), which can be conveniently subjected to recombinant DNA procedures and can bring about the expression of the polynucleotide. The choice of the vector will typically depend on the compatibility of the vector with the cell into which the vector is to be introduced. The vectors may be linear or closed circular plasmids. The vector may be an autonomously replicating vector, i.e., a vector, which exists as an extra-chromosomal entity, the replication of which is independent of chromosomal replication, e.g., a plasmid, an extra-chromosomal element, a mini-chromosome, or an artificial chromosome.
Alternatively, the vector may be one which, when introduced into the host cell, is integrated into the genome and replicated together with the chromosome(s) into which it has been integrated. The integrative cloning vector may integrate at random or at a predetermined target locus in the chromosomes of the host cell. A vector may comprise one or more selectable markers, which permit easy selection of transformed cells.
A recombinant host capable of producing a steviol glycoside which has been modified, preferably in its genome, to result in a deficiency in the production of a polypeptide described herein may be generated according to methods well known to those skilled in the art. A sequence encoding a polypeptide as described herein may be modified such that less or no expression of the polypeptide takes place. A sequence encoding a polypeptide as described herein may be partially or entirely deleted, for example.
A recombinant host of the invention may comprise any polypeptide as described herein. A recombinant host of the invention may overexpress or be deficient in any polypeptide described herein. Typically, a recombinant host of the invention is capable of producing a steviol glycoside. For example, a recombinant host of the invention may be capable of producing one or more of, for example, steviol-13-monoside, steviol-19-monoside, 13-[(β-D-Glucopyranosyl)oxy)kaur-16-en-18-oic acid 2-O-β-D-glucopyranosyl-β-D-glucopyranosyl ester, rubusoside, stevioside, steviol-19-diside, steviolbioside, rebA, rebE, rebD or rebM.
A recombinant host of the invention may comprise one or more recombinant nucleic acid sequences encoding one or more polypeptides having UDP-glycosyltransferase (UGT) activity.
For the purposes of this invention, a polypeptide having UGT activity is one which has glycosyltransferase activity (EC 2.4), i.e. that can act as a catalyst for the transfer of a monosaccharide unit from an activated nucleotide sugar (also known as the “glycosyl donor”) to a glycosyl acceptor molecule, usually an alcohol. The glycosyl donor for a UGT is typically the nucleotide sugar uridine diphosphate glucose (uracil-diphosphate glucose, UDP-glucose).
Such additional UGTs may be selected so as to produce a desired steviol glycoside. Schematic diagrams of steviol glycoside formation are set out in Humphrey et al., Plant Molecular Biology (2006) 61: 47-62 and Mohamed et al., J. Plant Physiology 168 (2011) 1136-1141. In addition,
A recombinant host of the invention may thus comprise one or more recombinant nucleic acid sequences encoding one or more of:
(i) a polypeptide having UGT74G1 activity;
(ii) a polypeptide having UGT2 activity;
(iii) a polypeptide having UGT85C2 activity; and
(iv) a polypeptide having UGT76G1 activity.
A recombinant yeast suitable for use in the invention may comprise a nucleotide sequence encoding a polypeptide capable of catalyzing the addition of a C-13-glucose to steviol. That is to say, a recombinant yeast suitable for use in a method of the invention may comprise a UGT which is capable of catalyzing a reaction in which steviol is converted to steviolmonoside.
Such a recombinant yeast suitable for use in a method of the invention may comprise a nucleotide sequence encoding a polypeptide having the activity shown by UDP-glycosyltransferase (UGT) UGT85C2, whereby the nucleotide sequence upon transformation of the yeast confers on that yeast the ability to convert steviol to steviolmonoside.
UGT85C2 activity is transfer of a glucose unit to the 13-OH of steviol. Thus, a suitable UGT85C2 may function as a uridine 5′-diphospho glucosyl: steviol 13-OH transferase, and a uridine 5′-diphospho glucosyl: steviol-19-0-glucoside 13-OH transferase. A functional UGT85C2 polypeptides may also catalyze glucosyl transferase reactions that utilize steviol glycoside substrates other than steviol and steviol-19-O-glucoside. Such sequences may be referred to as UGT1 sequences herein.
A recombinant yeast suitable for use in the invention may comprise a nucleotide sequence encoding a polypeptide which has UGT2 activity.
A polypeptide having UGT2 activity is one which functions as a uridine 5′-diphospho glucosyl: steviol-13-O-glucoside transferase (also referred to as a steviol-13-monoglucoside 1,2-glucosylase), transferring a glucose moiety to the C-2′ of the 13-O-glucose of the acceptor molecule, steviol-13-O-glucoside. Typically, a suitable UGT2 polypeptide also functions as a uridine 5′-diphospho glucosyl: rubusoside transferase transferring a glucose moiety to the C-2′ of the 13-O-glucose of the acceptor molecule, rubusoside.
A polypeptide having UGT2 activity may also catalyze reactions that utilize steviol glycoside substrates other than steviol-13-0-glucoside and rubusoside, e.g., functional UGT2 polypeptides may utilize stevioside as a substrate, transferring a glucose moiety to the C-2′ of the 19-O-glucose residue to produce rebaudioside E. A functional UGT2 polypeptides may also utilize rebaudioside A as a substrate, transferring a glucose moiety to the C-2′ of the 19-O-glucose residue to produce rebaudioside D. However, a functional UGT2 polypeptide may be one which does not transfer a glucose moiety to steviol compounds having a 1,3-bound glucose at the C-13 position, i.e., transfer of a glucose moiety to steviol 1,3-bioside and 1,3-stevioside typically does not occur.
A polypeptide having UGT2 activity may also transfer sugar moieties from donors other than uridine diphosphate glucose. For example, a polypeptide having UGT2 activity act as a uridine 5′-diphospho D-xylosyl: steviol-13-O-glucoside transferase, transferring a xylose moiety to the C-2′ of the 13-O-glucose of the acceptor molecule, steviol-13-O-glucoside. As another example, a polypeptide having UGT2 activity may act as a uridine 5′-diphospho L-rhamnosyl: steviol-13-0-glucoside transferase, transferring a rhamnose moiety to the C-2′ of the 13-O-glucose of the acceptor molecule, steviol.
A recombinant yeast suitable for use in the method of the invention may comprise a nucleotide sequence encoding a polypeptide having UGT activity may comprise a nucleotide sequence encoding a polypeptide capable of catalyzing the addition of a C-19-glucose to steviolbioside. That is to say, a recombinant yeast of the invention may comprise a UGT which is capable of catalyzing a reaction in which steviolbioside is converted to stevioside. Accordingly, such a recombinant yeast may be capable of converting steviolbioside to stevioside. Expression of such a nucleotide sequence may confer on the recombinant yeast the ability to produce at least stevioside.
A recombinant yeast suitable for use in a method of the invention may thus also comprise a nucleotide sequence encoding a polypeptide having the activity shown by UDP-glycosyltransferase (UGT) UGT74G1, whereby the nucleotide sequence upon transformation of the yeast confers on the cell the ability to convert steviolbioside to stevioside.
Suitable UGT74G1 polypeptides may be capable of transferring a glucose unit to the 13-OH and/or the 19-COOH of steviol. A suitable UGT74G1 polypeptide may function as a uridine 5′-diphospho glucosyl: steviol 19-COOH transferase and/or a uridine 5′-diphospho glucosyl: steviol-13-O-glucoside 19-COOH transferase. Functional UGT74G1 polypeptides also may catalyze glycosyl transferase reactions that utilize steviol glycoside substrates other than steviol and steviol-13-O-glucoside, or that transfer sugar moieties from donors other than uridine diphosphate glucose. Such sequences may be referred to herein as UGT3 sequences.
A recombinant yeast suitable for use in a method the invention may comprise a nucleotide sequence encoding a polypeptide capable of catalyzing glucosylation of the C-3′ of the glucose at the C-13 position of stevioside. That is to say, a recombinant yeast suitable for use in a method of the invention may comprise a UGT which is capable of catalyzing a reaction in which stevioside is converted to rebaudioside A. Accordingly, such a recombinant yeast may be capable of converting stevioside to rebaudioside A. Expression of such a nucleotide sequence may confer on the yeast the ability to produce at least rebaudioside A.
A recombinant yeast suitable for use in a method of the invention may thus also comprise a nucleotide sequence encoding a polypeptide having the activity shown by UDP-glycosyltransferase (UGT) UGT76G1, whereby the nucleotide sequence upon transformation of a yeast confers on that yeast the ability to convert stevioside to rebaudioside A.
A suitable UGT76G1 adds a glucose moiety to the C-3′ of the C-13-O-glucose of the acceptor molecule, a steviol 1,2 glycoside. Thus, UGT76G1 functions, for example, as a uridine 5′-diphospho glucosyl: steviol 13-0-1,2 glucoside C-3 ‘ glucosyl transferase and a uridine 5’-diphospho glucosyl: steviol-19-0-glucose, 13-0-1,2 bioside C-3′ glucosyl transferase. Functional UGT76G1 polypeptides may also catalyze glucosyl transferase reactions that utilize steviol glycoside substrates that contain sugars other than glucose, e.g., steviol rhamnosides and steviol xylosides. Such sequences may be referred to herein as UGT4 sequences. A UGT4 may alternatively or in addition be capable of converting RebD to RebM.
A recombinant yeast suitable for use in a method of the invention typically comprises nucleotide sequences encoding at least one polypeptide having UGT1 activity, at least one polypeptide having UGT2 activity, least one polypeptide having UGT3 activity and at least one polypeptide having UGT4 activity. One or more of these nucleic acid sequences may be recombinant. A given nucleic acid may encode a polypeptide having one or more of the above activities. For example, a nucleic acid encode for a polypeptide which has two, three or four of the activities set out above. Preferably, a recombinant yeast for use in the method of the invention comprises UGT1, UGT2 and UGT3 and UGT4 activity. Suitable UGT1, UGT2, UGT3 and UGT4 sequences are described in Table 1 of WO2015/007748.
A recombinant host of the invention may comprise two or more nucleic acid sequences encoding a polypeptide having any one UGT activity, for example UGT1, 2, 3 or 4, activity. Where a recombinant host of the invention comprises two or more nucleic acid sequence encoding a polypeptide having any one UGT activity, those nucleic acid sequences may be the same or different and/or may encode the same or different polypeptides. In particular, a recombinant host of the invention may comprise a nucleic acid sequence encoding a two different UGT2 polypeptides.
A recombinant host according to the invention may comprise one or more recombinant nucleotide sequence(s) encoding one of more of:
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- a polypeptide having ent-copalyl pyrophosphate synthase activity;
- a polypeptide having ent-Kaurene synthase activity;
- a polypeptide having ent-Kaurene oxidase activity; and
- a polypeptide having kaurenoic acid 13-hydroxylase activity.
For the purposes of this invention, a polypeptide having ent-copalyl pyrophosphate synthase (EC 5.5.1.13) is capable of catalyzing the chemical reaction:
This enzyme has one substrate, geranylgeranyl pyrophosphate, and one product, ent-copalyl pyrophosphate. This enzyme participates in gibberellin biosynthesis. This enzyme belongs to the family of isomerase, specifically the class of intramolecular lyases. The systematic name of this enzyme class is ent-copalyl-diphosphate lyase (decyclizing). Other names in common use include having ent-copalyl pyrophosphate synthase, ent-kaurene synthase A, and ent-kaurene synthetase A.
Suitable nucleic acid sequences encoding an ent-copalyl pyrophosphate synthase may for instance comprise a sequence as set out in SEQ ID. NO: 1, 3, 5, 7, 17, 19, 59, 61, 141, 142, 151, 152, 153, 154, 159, 160, 182 or 184 of WO2015/007748.
For the purposes of this invention, a polypeptide having ent-kaurene synthase activity (EC 4.2.3.19) is a polypeptide that is capable of catalyzing the chemical reaction:
ent-copalyl diphosphateent-kaurene+diphosphate
Hence, this enzyme has one substrate, ent-copalyl diphosphate, and two products, ent-kaurene and diphosphate.
This enzyme belongs to the family of lyases, specifically those carbon-oxygen lyases acting on phosphates. The systematic name of this enzyme class is ent-copalyl-diphosphate diphosphate-lyase (cyclizing, ent-kaurene-forming). Other names in common use include ent-kaurene synthase B, ent-kaurene synthetase B, ent-copalyl-diphosphate diphosphate-lyase, and (cyclizing). This enzyme participates in diterpenoid biosynthesis.
Suitable nucleic acid sequences encoding an ent-Kaurene synthase may for instance comprise a sequence as set out in SEQ ID. NO: 9, 11, 13, 15, 17, 19, 63, 65, 143, 144, 155, 156, 157, 158, 159, 160, 183 or 184 of WO2015/007748.
ent-copalyl diphosphate synthases may also have a distinct ent-kaurene synthase activity associated with the same protein molecule. The reaction catalyzed by ent-kaurene synthase is the next step in the biosynthetic pathway to gibberellins. The two types of enzymic activity are distinct, and site-directed mutagenesis to suppress the ent-kaurene synthase activity of the protein leads to build up of ent-copalyl pyrophosphate.
Accordingly, a single nucleotide sequence used in a recombinant host of the invention may encode a polypeptide having ent-copalyl pyrophosphate synthase activity and ent-kaurene synthase activity. Alternatively, the two activities may be encoded two distinct, separate nucleotide sequences.
For the purposes of this invention, a polypeptide having ent-kaurene oxidase activity (EC 1.14.13.78) is a polypeptide which is capable of catalysing three successive oxidations of the 4-methyl group of ent-kaurene to give kaurenoic acid. Such activity typically requires the presence of a cytochrome P450.
Suitable nucleic acid sequences encoding an ent-Kaurene oxidase may for instance comprise a sequence as set out in SEQ ID. NO: 21, 23, 25, 67, 85, 145, 161, 162, 163, 180 or 186 of WO2015/007748.
For the purposes of the invention, a polypeptide having kaurenoic acid 13-hydroxylase activity (EC 1.14.13) is one which is capable of catalyzing the formation of steviol (ent-kaur-16-en-13-ol-19-oic acid) using NADPH and O2. Such activity may also be referred to as ent-ka 13-hydroxylase activity.
Suitable nucleic acid sequences encoding a kaurenoic acid 13-hydroxylase may for instance comprise a sequence as set out in SEQ ID. NO: 27, 29, 31, 33, 69, 89, 91, 93, 95, 97, 146, 164, 165, 166, 167 or 185 of WO2015/007748.
A recombinant host of the invention may comprise a recombinant nucleic acid sequence encoding a polypeptide having NADPH-cytochrome p450 reductase activity. That is to say, a recombinant host of the invention may be capable of expressing a nucleotide sequence encoding a polypeptide having NADPH-cytochrome p450 reductase activity. For the purposes of the invention, a polypeptide having NADPH-Cytochrome P450 reductase activity (EC 1.6.2.4; also known as NADPH:ferrihemoprotein oxidoreductase, NADPH:hemoprotein oxidoreductase, NADPH:P450 oxidoreductase, P450 reductase, POR, CPR, CYPOR) is typically one which is a membrane-bound enzyme allowing electron transfer to cytochrome P450 in the microsome of the eukaryotic cell from a FAD- and FMN-containing enzyme NADPH:cytochrome P450 reductase (POR; EC 1.6.2.4).
In a recombinant host of the invention, the ability of the host to produce geranylgeranyl diphosphate (GGPP) may be upregulated. Upregulated in the context of this invention implies that the recombinant host produces more GGPP than an equivalent non-recombinant host.
Accordingly, a recombinant host of the invention may comprise one or more nucleotide sequence(s) encoding hydroxymethylglutaryl-CoA reductase, farnesyl-pyrophosphate synthetase and geranylgeranyl diphosphate synthase, whereby the nucleotide sequence(s) upon transformation of a host confer(s) on that host the ability to produce elevated levels of GGPP.
Thus, a recombinant host according to the invention may comprise one or more recombinant nucleic acid sequence(s) encoding one or more of hydroxymethylglutaryl-CoA reductase, farnesyl-pyrophosphate synthetase and geranylgeranyl diphosphate synthase.
Accordingly, a recombinant host of the invention may comprise nucleic acid sequences encoding one or more of:
a polypeptide having hydroxymethylglutaryl-CoA reductase activity;
a polypeptide having farnesyl-pyrophosphate synthetase activity; and
A recombinant host of the invention may be, for example, an multicellular organism or a cell thereof or a unicellular organism. A host of the invention may be a prokaryotic, archaebacterial or eukaryotic host cell.
A prokaryotic host cell may, but is not limited to, a bacterial host cell. An eukaryotic host cell may be, but is not limited to, a yeast, a fungus, an amoeba, an algae, an animal, an insect host cell.
An eukaryotic host cell may be a fungal host cell. “Fungi” include all species of the subdivision Eumycotina (Alexopoulos, C. J., 1962, In: Introductory Mycology, John Wiley & Sons, Inc., New York). The term fungus thus includes among others filamentous fungi and yeast.
“Filamentous fungi” are herein defined as eukaryotic microorganisms that include all filamentous forms of the subdivision Eumycotina and Oomycota (as defined by Hawksworth et al., 1995, supra). The filamentous fungi are characterized by a mycelial wall composed of chitin, cellulose, glucan, chitosan, mannan, and other complex polysaccharides. Vegetative growth is by hyphal elongation and carbon catabolism is obligatory aerobic. Filamentous fungal strains include, but are not limited to, strains of Acremonium, Aspergillus, Agaricus, Aureobasidium, Cryptococcus, Corynascus, Chrysosporium, Filibasidium, Fusarium, Humicola, Magnaporthe, Monascus, Mucor, Myceliophthora, Mortierella, Neocallimastix, Neurospora, Paecilomyces, Penicillium, Piromyces, Phanerochaete Podospora, Pycnoporus, Rhizopus, Schizophyllum, Sordaria, Talaromyces, Rasmsonia, Thermoascus, Thielavia, Tolypocladium, Trametes and Trichoderma. Preferred filamentous fungal strains that may serve as host cells belong to the species Aspergillus niger, Aspergillus oryzae, Aspergillus fumigatus, Penicillium chrysogenum, Penicillium citrinum, Acremonium chrysogenum, Trichoderma reesei, Rasamsonia emersonii (formerly known as Talaromyces emersonii), Aspergillus sojae, Chrysosporium lucknowense, Myceliophtora thermophyla. Reference host cells for the comparison of fermentation characteristics of transformed and untransformed cells, include e.g. Aspergillus niger CBS120.49, CBS 513.88, Aspergillus oryzae ATCC16868, ATCC 20423, IFO 4177, ATCC 1011, ATCC 9576, ATCC14488-14491, ATCC 11601, ATCC12892, Aspergillus fumigatus AF293 (CBS101355), P. chrysogenum CBS 455.95, Penicillium citrinum ATCC 38065, Penicillium chrysogenum P2, Acremonium chrysogenum ATCC 36225, ATCC 48272, Trichoderma reesei ATCC 26921, ATCC 56765, ATCC 26921, Aspergillus sojae ATCC11906, Chrysosporium lucknowense ATCC44006 and derivatives of all of these strains. Particularly preferred as filamentous fungal host cell are Aspergillus niger CBS 513.88 and derivatives thereof.
An eukaryotic host cell may be a yeast cell. Preferred yeast host cells may be selected from the genera: Saccharomyces (e.g., S. cerevisiae, S. bayanus, S. pastorianus, S. carlsbergensis), Brettanomyces, Kluyveromyces, Candida (e.g., C. krusei, C. revkaufi, C. pulcherrima, C. tropicalis, C. utilis), Issatchenkia (eg. I. orientalis) Pichia (e.g., P. pastoris and P. kudriavzevii), Schizosaccharomyces, Hansenula, Kloeckera, Pachysolen, Schwanniomyces, Trichosporon, Yarrowia (e.g., Y. lipolytica (formerly classified as Candida lipolytica)), Yamadazyma.
Prokaryotic host cells may be bacterial host cells. Bacterial host cell may be Gram negative or Gram positive bacteria. Examples of bacteria include, but are not limited to, bacteria belonging to the genus Bacillus (e.g., B. subtilis, B. amyloliquefaciens, B. licheniformis, B. puntis, B. megaterium, B. halodurans, B. pumilus), Acinetobacter, Nocardia, Xanthobacter, Escherichia (e.g., E. coli (e.g., strains DH 1 OB, Stbl2, DH5-alpha, DB3, DB3.1), DB4, DB5, JDP682 and ccdA-over (e.g., U.S. application Ser. No. 09/518,188))), Streptomyces, Erwinia, Klebsiella, Serratia (e.g., S. marcessans), Pseudomonas (e.g., P. aeruginosa), Salmonella (e.g., S. typhimurium, S. typhi). Bacteria also include, but are not limited to, photosynthetic bacteria (e.g., green non-sulfur bacteria (e.g., Choroflexus bacteria (e.g., C. aurantiacus), Chloronema (e.g., C. gigateum)), green sulfur bacteria (e.g., Chlorobium bacteria (e.g., C. limicola), Pelodictyon (e.g., P. luteolum), purple sulfur bacteria (e.g., Chromatium (e.g., C. okenii)), and purple non-sulfur bacteria (e.g., Rhodospirillum (e.g., R. rubrum), Rhodobacter (e.g. R. sphaeroides, R. capsulatus), and Rhodomicrobium bacteria (e.g., R. vanellii)).
Host Cells may be host cells from non-microbial organisms. Examples of such cells, include, but are not limited to, insect cells (e.g., Drosophila (e.g., D. melanogaster), Spodoptera (e.g., S. frugiperda Sf9 or Sf21 cells) and Trichoplusa (e.g., High-Five cells); nematode cells (e.g., C. elegans cells); avian cells; amphibian cells (e.g., Xenopus laevis cells); reptilian cells; and mammalian cells (e.g., NIH3T3, 293, CHO, COS, VERO, C127, BHK, Per-C6, Bowes melanoma and HeLa cells).
A recombinant host according to the present invention may be able to grow on any suitable carbon source known in the art and convert it to a steviol glycoside. The recombinant host may be able to convert directly plant biomass, celluloses, hemicelluloses, pectines, rhamnose, galactose, fucose, maltose, maltodextrines, ribose, ribulose, or starch, starch derivatives, sucrose, lactose and glycerol. Hence, a preferred host expresses enzymes such as cellulases (endocellulases and exocellulases) and hemicellulases (e.g. endo- and exo-xylanases, arabinases) necessary for the conversion of cellulose into glucose monomers and hemicellulose into xylose and arabinose monomers, pectinases able to convert pectines into glucuronic acid and galacturonic acid or amylases to convert starch into glucose monomers. Preferably, the host is able to convert a carbon source selected from the group consisting of glucose, xylose, arabinose, sucrose, lactose and glycerol. The host cell may for instance be a eukaryotic host cell as described in WO03/062430, WO06/009434, EP1499708B1, WO2006096130 or WO04/099381.
Thus, in a further aspect, the invention also provides a process for the preparation of a steviol glycoside which comprises fermenting a recombinant host of the invention which is capable of producing at least one steviol glycoside in a suitable fermentation medium, and optionally recovering the steviol glycoside.
The fermentation medium used in the process for the production of a steviol glycoside may be any suitable fermentation medium which allows growth of a particular eukaryotic host cell. The essential elements of the fermentation medium are known to the person skilled in the art and may be adapted to the host cell selected.
Preferably, the fermentation medium comprises a carbon source selected from the group consisting of plant biomass, celluloses, hemicelluloses, pectines, rhamnose, galactose, fucose, fructose, maltose, maltodextrines, ribose, ribulose, or starch, starch derivatives, sucrose, lactose, fatty acids, triglycerides and glycerol. Preferably, the fermentation medium also comprises a nitrogen source such as ureum, or an ammonium salt such as ammonium sulphate, ammonium chloride, ammoniumnitrate or ammonium phosphate.
The fermentation process according to the present invention may be carried out in batch, fed-batch or continuous mode. A separate hydrolysis and fermentation (SHF) process or a simultaneous saccharification and fermentation (SSF) process may also be applied. A combination of these fermentation process modes may also be possible for optimal productivity. A SSF process may be particularly attractive if starch, cellulose, hemicelluose or pectin is used as a carbon source in the fermentation process, where it may be necessary to add hydrolytic enzymes, such as cellulases, hemicellulases or pectinases to hydrolyse the substrate.
The recombinant host used in the process for the preparation of a steviol glycoside may be any suitable recombinant host as defined herein above. It may be advantageous to use a recombinant eukaryotic recombinant host according to the invention in the process since most eukaryotic cells do not require sterile conditions for propagation and are insensitive to bacteriophage infections. In addition, eukaryotic host cells may be grown at low pH to prevent bacterial contamination.
The recombinant host according to the present invention may be a facultative anaerobic microorganism. A facultative anaerobic recombinant host can be propagated aerobically to a high cell concentration. This anaerobic phase can then be carried out at high cell density which reduces the fermentation volume required substantially, and may minimize the risk of contamination with aerobic microorganisms.
The fermentation process for the production of a steviol glycoside according to the present invention may be an aerobic or an anaerobic fermentation process.
An anaerobic fermentation process may be herein defined as a fermentation process run in the absence of oxygen or in which substantially no oxygen is consumed, preferably less than 5, 2.5 or 1 mmol/L/h, and wherein organic molecules serve as both electron donor and electron acceptors. The fermentation process according to the present invention may also first be run under aerobic conditions and subsequently under anaerobic conditions.
The fermentation process may also be run under oxygen-limited, or micro-aerobical, conditions. Alternatively, the fermentation process may first be run under aerobic conditions and subsequently under oxygen-limited conditions. An oxygen-limited fermentation process is a process in which the oxygen consumption is limited by the oxygen transfer from the gas to the liquid. The degree of oxygen limitation is determined by the amount and composition of the ingoing gasflow as well as the actual mixing/mass transfer properties of the fermentation equipment used.
The production of a steviol glycoside in the process according to the present invention may occur during the growth phase of the host cell, during the stationary (steady state) phase or during both phases. It may be possible to run the fermentation process at different temperatures.
The process for the production of a steviol glycoside may be run at a temperature which is optimal for the recombinant host. The optimum growth temperature may differ for each transformed recombinant host and is known to the person skilled in the art. The optimum temperature might be higher than optimal for wild type organisms to grow the organism efficiently under non-sterile conditions under minimal infection sensitivity and lowest cooling cost. Alternatively, the process may be carried out at a temperature which is not optimal for growth of the recombinant host.
The process for the production of a steviol glycoside according to the present invention may be carried out at any suitable pH value. If the recombinant host is a yeast, the pH in the fermentation medium preferably has a value of below 6, preferably below 5,5, preferably below 5, preferably below 4,5, preferably below 4, preferably below pH 3,5 or below pH 3,0, or below pH 2,5, preferably above pH 2. An advantage of carrying out the fermentation at these low pH values is that growth of contaminant bacteria in the fermentation medium may be prevented.
Such a process may be carried out on an industrial scale. The product of such a process is one or more steviol glycosides.
Recovery of steivol glycoside(s) from the fermentation medium may be performed by known methods in the art, for instance by distillation, vacuum extraction, solvent extraction, or evaporation.
In the process for the production of a steviol glycoside according to the invention, it may be possible to achieve a concentration of above 5 mg/l fermentation broth, preferably above 10 mg/l, preferably above 20 mg/l, preferably above 30 mg/l fermentation broth, preferably above 40 mg/l, more preferably above 50 mg/l, preferably above 60 mg/l, preferably above 70, preferably above 80 mg/l, preferably above 100 mg/l, preferably above 1 g/I, preferably above 5 g/I, preferably above 10 g/I, for example at least about 15 g/L, such as at least about 20 g/I. The invention further provides a fermentation broth comprising a steviol glycoside obtainable by the process of the invention for the preparation of a steivol glycoside.
In the event that one or more steviol glycosides is expressed within a recombinant host of the invention, such cells may need to be treated so as to release them. Preferentially, at least one steviol glycoside, for example rebA or rebM, is produced extracellularly
The invention also provides a steviol glycoside obtained by a process according to the invention for the preparation of a steviol glycoside or obtainable from a fermentation broth of the invention. Such a steviol glycoside may be a non-naturally occurring steviol glycoside, that is to say one which is not produced in plants.
Also provided is a composition obtainable by a process of the invention (which typically comprises one or more steviol glycosides). Also provided is a composition comprising two or more steviol glycosides obtainable by a process of the invention for the preparation of a steviol glycoside or obtainable from a fermentation broth of the invention. In such a composition, one or more of the steviol glycosides may be a non-naturally occurring steviol glycoside, that is to say one which is not produced in plants. These are all compositions of the invention.
A composition of the invention may be used in any application known for such compounds. In particular, such a composition may for instance be used as a sweetener, for example in a food or a beverage. According to the invention therefore, there is provided a foodstuff, feed or beverage which comprises a composition of the invention.
For example a composition of the invention may be formulated in soft drinks, as a tabletop sweetener, chewing gum, dairy product such as yoghurt (eg. plain yoghurt), cake, cereal or cereal-based food, nutraceutical, pharmaceutical, edible gel, confectionery product, cosmetic, toothpastes or other oral cavity composition, etc. In addition, a composition of the invention can be used as a sweetener not only for drinks, foodstuffs, and other products dedicated for human consumption, but also in animal feed and fodder with improved characteristics.
Accordingly, the invention provides, inter alia, a foodstuff, feed or beverage which comprises a composition of the invention.
During the manufacturing of foodstuffs, drinks, pharmaceuticals, cosmetics, table top products, chewing gum the conventional methods such as mixing, kneading, dissolution, pickling, permeation, percolation, sprinkling, atomizing, infusing and other methods can be used.
A composition of the invention can be used in dry or liquid forms. It can be added before or after heat treatment of food products. The amount of the sweetener depends on the purpose of usage. It can be added alone or in the combination with other compounds.
A composition of the invention may be blended with one or more further non-caloric or caloric sweeteners. Such blending may be used to improve flavour or temporal profile or stability. A wide range of both non-caloric and caloric sweeteners may be suitable for blending with a composition of the invention. For example, non-caloric sweeteners such as mogroside, monatin, aspartame, acesulfame salts, cyclamate, sucralose, saccharin salts or erythritol. Caloric sweeteners suitable for blending with a steviol glycoside or a composition of the invention include sugar alcohols and carbohydrates such as sucrose, glucose, fructose and HFCS. Sweet tasting amino acids such as glycine, alanine or serine may also be used.
A composition of the invention can be used in the combination with a sweetener suppressor, such as a natural sweetener suppressor. It may be combined with an umami taste enhancer, such as an amino acid or a salt thereof.
A composition of the invention can be combined with a polyol or sugar alcohol, a carbohydrate, a physiologically active substance or functional ingredient (for example a carotenoid, dietary fiber, fatty acid, saponin, antioxidant, nutraceutical, flavonoid, isothiocyanate, phenol, plant sterol or stanol (phytosterols and phytostanols), a polyols, a prebiotic, a probiotic, a phytoestrogen, soy protein, sulfides/thiols, amino acids, a protein, a vitamin, a mineral, and/or a substance classified based on a health benefits, such as cardiovascular, cholesterol-reducing or anti-inflammatory.
A composition of the invention may include a flavoring agent, an aroma component, a nucleotide, an organic acid, an organic acid salt, an inorganic acid, a bitter compound, a protein or protein hydrolyzate, a surfactant, a flavonoid, an astringent compound, a vitamin, a dietary fiber, an antioxidant, a fatty acid and/or a salt.
A composition of the invention may be applied as a high intensity sweetener to produce zero calorie, reduced calorie or diabetic beverages and food products with improved taste characteristics. Also it can be used in drinks, foodstuffs, pharmaceuticals, and other products in which sugar cannot be used.
In addition, a composition of the invention may be used as a sweetener not only for drinks, foodstuffs, and other products dedicated for human consumption, but also in animal feed and fodder with improved characteristics.
The examples of products where a composition of the invention can be used as a sweetening compound can be as alcoholic beverages such as vodka, wine, beer, liquor, sake, etc; natural juices, refreshing drinks, carbonated soft drinks, diet drinks, zero calorie drinks, reduced calorie drinks and foods, yogurt drinks, instant juices, instant coffee, powdered types of instant beverages, canned products, syrups, fermented soybean paste, soy sauce, vinegar, dressings, mayonnaise, ketchups, curry, soup, instant bouillon, powdered soy sauce, powdered vinegar, types of biscuits, rice biscuit, crackers, bread, chocolates, caramel, candy, chewing gum, jelly, pudding, preserved fruits and vegetables, fresh cream, jam, marmalade, flower paste, powdered milk, ice cream, sorbet, vegetables and fruits packed in bottles, canned and boiled beans, meat and foods boiled in sweetened sauce, agricultural vegetable food products, seafood, ham, sausage, fish ham, fish sausage, fish paste, deep fried fish products, dried seafood products, frozen food products, preserved seaweed, preserved meat, tobacco, medicinal products, and many others. In principal it can have unlimited applications.
The sweetened composition comprises a beverage, non-limiting examples of which include non-carbonated and carbonated beverages such as colas, ginger ales, root beers, ciders, fruit-flavored soft drinks (e.g., citrus-flavored soft drinks such as lemon-lime or orange), powdered soft drinks, and the like; fruit juices originating in fruits or vegetables, fruit juices including squeezed juices or the like, fruit juices containing fruit particles, fruit beverages, fruit juice beverages, beverages containing fruit juices, beverages with fruit flavorings, vegetable juices, juices containing vegetables, and mixed juices containing fruits and vegetables; sport drinks, energy drinks, near water and the like drinks (e.g., water with natural or synthetic flavorants); tea type or favorite type beverages such as coffee, cocoa, black tea, green tea, oolong tea and the like; beverages containing milk components such as milk beverages, coffee containing milk components, cafe au lait, milk tea, fruit milk beverages, drinkable yogurt, lactic acid bacteria beverages or the like; and dairy products.
Generally, the amount of sweetener present in a sweetened composition varies widely depending on the particular type of sweetened composition and its desired sweetness. Those of ordinary skill in the art can readily discern the appropriate amount of sweetener to put in the sweetened composition.
During the manufacturing of foodstuffs, drinks, pharmaceuticals, cosmetics, table top products, chewing gum the conventional methods such as mixing, kneading, dissolution, pickling, permeation, percolation, sprinkling, atomizing, infusing and other methods can be used.
Thus, compositions which incorporate a composition of the invention can be made by any method known to those skilled in the art that provide homogenous even or homogeneous mixtures of the ingredients. These methods include dry blending, spray drying, agglomeration, wet granulation, compaction, co-crystallization and the like.
In solid form a composition of the invention can be provided to consumers in any form suitable for delivery into the comestible to be sweetened, including sachets, packets, bulk bags or boxes, cubes, tablets, mists, or dissolvable strips. The composition can be delivered as a unit dose or in bulk form.
For liquid sweetener systems and compositions convenient ranges of fluid, semi-fluid, paste and cream forms, appropriate packing using appropriate packing material in any shape or form shall be invented which is convenient to carry or dispense or store or transport any combination containing any of the above sweetener products or combination of product produced above.
A composition of the invention may include various bulking agents, functional ingredients, colorants, flavors.
The terms “sequence homology” or “sequence identity” or “homology” or “identity” are used interchangeably herein. For the purpose of this invention, it is defined here that in order to determine the percentage of sequence homology or sequence identity of two amino acid sequences or of two nucleic acid sequences, the sequences are aligned for optimal comparison purposes. In order to optimize the alignment between the two sequences gaps may be introduced in any of the two sequences that are compared. Such alignment can be carried out over the full length of the sequences being compared. Alternatively, the alignment may be carried out over a shorter length, for example over about 20, about 50, about 100 or more nucleic acids/based or amino acids. The sequence identity is the percentage of identical matches between the two sequences over the reported aligned region.
A comparison of sequences and determination of percentage of sequence identity between two sequences can be accomplished using a mathematical algorithm. The skilled person will be aware of the fact that several different computer programs are available to align two sequences and determine the identity between two sequences (Kruskal, J. B. (1983) An overview of sequence comparison In D. Sankoff and J. B. Kruskal, (ed.), Time warps, string edits and macromolecules: the theory and practice of sequence comparison, pp. 1-44 Addison Wesley). The percent sequence identity between two amino acid sequences or between two nucleotide sequences may be determined using the Needleman and Wunsch algorithm for the alignment of two sequences. (Needleman, S. B. and Wunsch, C. D. (1970) J. Mol. Biol. 48, 443-453). Both amino acid sequences and nucleotide sequences can be aligned by the algorithm. The Needleman-Wunsch algorithm has been implemented in the computer program NEEDLE. For the purpose of this invention the NEEDLE program from the EMBOSS package was used (version 2.8.0 or higher, EMBOSS: The European Molecular Biology Open Software Suite (2000) Rice, P. Longden, I. and Bleasby, A. Trends in Genetics 16, (6) pp 276-277, http://emboss.bioinformatics.nl/). For protein sequences EBLOSUM62 is used for the substitution matrix. For nucleotide sequence, EDNAFULL is used. The optional parameters used are a gap-open penalty of 10 and a gap extension penalty of 0.5. The skilled person will appreciate that all these different parameters will yield slightly different results but that the overall percentage identity of two sequences is not significantly altered when using different algorithms.
After alignment by the program NEEDLE as described above the percentage of sequence identity between a query sequence and a sequence of the invention is calculated as follows: Number of corresponding positions in the alignment showing an identical amino acid or identical nucleotide in both sequences divided by the total length of the alignment after subtraction of the total number of gaps in the alignment. The identity defined as herein can be obtained from NEEDLE by using the NOBRIEF option and is labeled in the output of the program as “longest-identity”.
The nucleic acid and protein sequences of the present invention can further be used as a “query sequence” to perform a search against public databases to, for example, identify other family members or related sequences. Such searches can be performed using the NBLAST and XBLAST programs (version 2.0) of Altschul, et al. (1990) J. Mol. Biol. 215:403-10. BLAST nucleotide searches can be performed with the NBLAST program, score=100, wordlength=12 to obtain nucleotide sequences homologous to nucleic acid molecules of the invention. BLAST protein searches can be performed with the XBLAST program, score=50, wordlength=3 to obtain amino acid sequences homologous to protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., (1997) Nucleic Acids Res. 25(17): 3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See the homepage of the National Center for Biotechnology Information at http://www.ncbi.nlm.nih.gov/.
Standard genetic techniques, such as overexpression of enzymes in the host cells, genetic modification of host cells, or hybridisation techniques, are known methods in the art, such as described in Sambrook and Russel (2001) “Molecular Cloning: A Laboratory Manual (3rd edition), Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, or F. Ausubel et al, eds., “Current protocols in molecular biology”, Green Publishing and Wiley Interscience, New York (1987). Methods for transformation, genetic modification etc of fungal host cells are known from e.g. EP-A-0 635 574, WO 98/46772, WO 99/60102 and WO 00/37671, WO90/14423, EP-A-0481008, EP-A-0635 574 and U.S. Pat. No. 6,265,186.
Embodiments of the Invention
- 1. A recombinant host capable of producing a steviol glycoside which overexpresses a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
- 2. A recombinant host capable of producing a steviol glycoside which has been modified, preferably in its genome, to result in a deficiency in the production of a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
- 3. A recombinant host according to embodiment 1, which comprises a recombinant nucleic acid encoding a polypeptide which comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
- 4. A recombinant host according to any one of the preceding embodiments which comprises one or more recombinant nucleotide sequence(s) encoding:
- a polypeptide having ent-copalyl pyrophosphate synthase activity;
- a polypeptide having ent-Kaurene synthase activity;
- a polypeptide having ent-Kaurene oxidase activity; and
- a polypeptide having kaurenoic acid 13-hydroxylase activity.
- 5. A recombinant host according to any one of the preceding embodiments, which comprises a recombinant nucleic acid sequence encoding a polypeptide having NADPH-cytochrome p450 reductase activity.
- 6. A recombinant host according to any one of the preceding embodiments which comprises a recombinant nucleic acid sequence encoding one or more of:
- (i) a polypeptide having UGT74G1 activity;
- (ii) a polypeptide having UGT2 activity;
- (iii) a polypeptide having UGT85C2 activity; and
- (iv) a polypeptide having UGT76G1 activity.
- 7. A recombinant host according to any one of the preceding embodiments, wherein the host belongs to one of the genera Saccharomyces, Aspergillus, Pichia, Kluyveromyces, Candida, Hansenula, Humicola, Issatchenkia, Trichosporon, Brettanomyces, Pachysolen, Yarrowia, Yamadazyma or Escherichia.
- 8. A recombinant host according to embodiment 7, wherein the recombinant host is a Saccharomyces cerevisiae cell, a Yarrowia lipolitica cell, a Candida krusei cell, an Issatchenkia orientalis cell or an Escherichia coli cell.
- 9. A recombinant host according to any one of the preceding embodiments, wherein the ability of the host to produce geranylgeranyl diphosphate (GGPP) is upregulated.
- 10. A recombinant host according to any one of the preceding embodiments which comprises a nucleic acid sequence encoding one or more of:
- a polypeptide having hydroxymethylglutaryl-CoA reductase activity; or
- a polypeptide having farnesyl-pyrophosphate synthetase activity.
- 11. A recombinant host capable of producing a steviol glycoside which overexpresses a heterologous polypeptide which mediates steviol glycoside transport.
- 12. A process for the preparation of a steviol glycoside which comprises fermenting a recombinant host according to any one of the preceding embodiments in a suitable fermentation medium and, optionally, recovering the steviol glycoside.
- 13. A process according to embodiment 12 for the preparation of a steviol glycoside, optionally wherein the process is carried out on an industrial scale.
- 14. A fermentation broth comprising a steviol glycoside obtainable by the process according to embodiment 12 or 13.
- 15. A steviol glycoside obtained by a process according to embodiment 12 or 13 or obtained from a fermentation broth according to embodiment 14.
- 16. A composition obtainable by a process according to embodiment 12 or 13, a composition comprising two or more steviol glycosides obtained by a process according to embodiment 12 or 13 or a composition obtained from a fermentation broth according to embodiment 14.
- 17. A foodstuff, feed or beverage which comprises a steviol glycoside according to claim 15 or a composition according to claim 16.
A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.
The disclosure of each reference set forth herein is incorporated herein by reference in its entirety.
The present invention is further illustrated by the following Examples:
EXAMPLES GeneralStandard genetic techniques, such as overexpression of enzymes in the host cells, as well as for additional genetic modification of host cells, are known methods in the art, such as described in Sambrook and Russel (2001) “Molecular Cloning: A Laboratory Manual (3rd edition), Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, or F. Ausubel et al, eds., “Current protocols in molecular biology”, Green Publishing and Wiley Interscience, New York (1987). Methods for transformation and genetic modification of fungal host cells are known from e.g. EP-A-0 635 574, WO 98/46772, WO 99/60102 and WO 00/37671.
Example 1: Over-Expression of ERG20, BTS1 and tHMG in S. cerevisiaeFor over-expression of ERG20, BTS1 tHMG1, expression cassettes were designed to be integrated in one locus using technology described in WO2013/076280. To amplify the 5′ and 3′ integration flanks for the integration locus, suitable primers and genomic DNA from a CEN.PK yeast strain (van Dijken et al. Enzyme and Microbial Technology 26 (2000) 706-714) was used. The different genes were ordered as cassettes (containing homologous sequence, promoter, gene, terminator, homologous sequence) at DNA2.0. The genes in these cassettes were flanked by constitutive promoters and terminators. See Table 1. Plasmid DNA from DNA2.0 containing the ERG20, tHMG1 and BTS1 cassettes were dissolved to a concentration of 100 ng/μl. In a 50 μl PCR mix 20 ng template was used together with 20 pmol of the primers. The material was dissolved to a concentration of 0.5 μg/μl.
For amplification of the selection marker, the pUG7-EcoRV construct (
After transformation and recovery for 2.5 hours in YEPhD (yeast extract phytone peptone glucose; BBL Phytone Peptone from BD) at 30° C. the cells were plated on YEPhD agar with 200 μg/ml G418 (Sigma). The plates were incubated at 30° C. for 4 days. Correct integration was established with diagnostic PCR and sequencing. Over-expression was confirmed with LC/MS on the proteins. The schematic of the assembly of ERG20, tHMG1 and BTS1 is illustrated in
Expression of CRE-recombinase in this strain led to out-recombination of the KanMX marker. Correct out-recombination, and presence of ERG20, tHMG and BTS1 was established with diagnostic PCR.
Example 2. Knock Down of Erg9For reducing the expression of Erg9, an Erg9 knock down construct was designed and used that contains a modified 3′ end, that continues into the TRP1 promoter driving TRP1 expression.
The construct containing the Erg9-KD fragment was transformed to E. coli TOP10 cells. Transformants were grown in 2PY (2 times Phytone peptone Yeast extract), sAMP medium. Plasmid DNA was isolated with the QIAprep Spin Miniprep kit (Qiagen) and digested with Sall-HF (New England Biolabs). To concentrate, the DNA was precipitated with ethanol. The fragment was transformed to S. cerevisiae, and colonies were plated on mineral medium (Verduyn et al, 1992. Yeast 8:501-517) agar plates without tryptophan. Correct integration of the Erg9-KD construct was confirmed with diagnostic PCR and sequencing. The schematic of performed transformation of the Erg9-KD construct is illustrated in
For over-expression of UGT2_1a, technology was used as described in patent application nos. WO2013/076280 and WO2013/144257. The UGT2_1a was ordered as a cassette (containing homologous sequence, promoter, gene, terminator, homologous sequence) at DNA2.0. For details, see Table 3. To obtain the fragments containing the marker and Cre-recombinase, technology was used as described in patent application no. WO2013/135728. The NAT marker, conferring resistance to nourseothricin was used for selection.
Suitable primers were used for amplification. To amplify the 5′ and 3′ integration flanks for the integration locus, suitable primers and genomic DNA from a CEN.PK yeast strain was used.
S. cerevisiae yeast strain STV003 was transformed with the fragments listed in Table 4, and the transformation mix was plated on YEPhD agar plates containing 50 μg/ml nourseothricin (Lexy NTC from Jena Bioscience).
Expression of the CRE recombinase is activated by the presence of galactose. To induce the expression of the CRE recombinase, transformants were restreaked on YEPh Galactose medium. This resulted in out-recombination of the marker(s) located between lox sites. Correct integration of the UGT2_1a and out-recombination of the NAT marker was confirmed with diagnostic PCR. The resulting strain was named STV004. The schematic of the performed transformation of the UGT2_1a construct is illustrated in
All pathway genes leading to the production of RebA were designed to be integrated in one locus using technology described in patent application nos. WO2013/076280 and WO2013/144257. To amplify the 5′ and 3′ integration flanks for the integration locus, suitable primers and genomic DNA from a CEN.PK yeast strain was used. The different genes were ordered as cassettes (containing homologous sequence, promoter, gene, terminator, homologous sequence) at DNA2.0 (see Table 5 for overview). The DNA from DNA2.0 was dissolved to 100 ng/μl. This stock solution was further diluted to 5 ng/μl, of which 1 μl was used in a 50 μl-PCR mixture. The reaction contained 25 pmol of each primer. After amplification, DNA was purified with the NucleoSpin 96 PCR Clean-up kit (Macherey-Nagel) or alternatively concentrated using ethanol precipitation.
All fragments for the pathway to RebA, the marker and the flanks (see overview in Table 6) were transformed to S. cerevisiae yeast strain STV004. After overnight recovery in YEPhD at 20° C. the transformation mixes were plated on YEPhD agar containing 200 μg/ml G418. These were incubated 3 days at 25° C. and one night at RT.
Correct integration was confirmed with diagnostic PCR and sequence analysis (3500 Genetic Analyzer, Applied Biosystems). The sequence reactions were done with the BigDye Terminator v3.1 Cycle Sequencing kit (Life Technologies). Each reaction (10 μl) contained 50 ng template and 3.2 pmol primer. The products were purified by ethanol/EDTA precipitation, dissolved in 10 μl HiDi formamide and applied onto the apparatus. The strain was named STV016. The schematic of how the pathway from GGPP to RebA is integrated into the genome is illustrated in
To remove the KanMX marker from the chromosome of strain STV016, this strain was transformed with plasmid pSH65, expressing Cre-recombinase (Guldender, 2002). Subsequently plasmid pSH65 was cured from the strain by growing on non-selective medium (YEP 2% glucose). The resulting, KanMX-free and pSH65-free strains, as determined by plating on plates containing 200 μg G418/ml or 20 μg phleomycin/ml, where no growth should occur, was named STV027. Absence of the KanMX marker was furthermore confirmed with diagnostic PCR. The resulting strain was named STV027.
Example 6: Construction of Strain STV035To introduce additional copies of KAH and CPR available PCR fragments were used (see Table 6 and Table 7). The KanMX selection marker fragment was amplified from pUG7-EcoRV (
STV027 was transformed with these fragments (Table 7) according the Gietz method. After 2 h recovery in YEPhD at 30° C. the transformation mixes were plated on YEPhD agar containing 200 μg/ml G418. These were incubated for 4 days at 30° C.
The schematic of how KAH and CPR are integrated into the genome is illustrated in
For the integration of a second copy of CPS this gene was amplified together with a TDH3 promoter and ADH2 terminator.
Due to presence of a KanMX marker in STV035 a NAT marker was amplified from pUG7-NAT (
The different fragments for integration of the second copy of CPS (Table 9) were combined and transformed to STV035. After recovery the transformation mix was plated on YEPhD agar plates containing 50 μg/ml nourseothricin. These were incubated for 3 days at 30° C. Correct integration was confirmed with diagnostic PCR. The new strain was named STV058. The schematic of how the CPS is integrated into the genome is illustrated in
For expression of ALNQ_007_38000 (SEQ ID NO: 33) and ALNQ_214_12000 (SEQ ID NO: 36), expression cassettes were designed to be integrated in the S. cerevisiae STV058 Chr01.05 locus, using technology described in patent application nos. WO2013/076280 and WO2013/144257. To amplify the 5′ and 3′ integration flanks for the integration locus, suitable primers and genomic DNA from a CEN.PK yeast strain were used.
The two transporter genes were amplified from I. orientalis CBS 5147 genomic DNA using suitable primers. The PCR amplicons were sub-cloned in a in a Zero Blunt TOPO vector (Life Technologies). The genes were cloned into the Sc_2_5-2_a.bbn vector using BspMI or BsaI in which they were flanked by the constitutive promoters KI_ENO1 or Sc_GPM1 and Sc_TAL1 terminator resulting in two expression cassettes for each transporter gene. The expression cassettes were PCR-amplified in six times 50 μl PCR mix. The PCR product was purified and concentrated using NucleoSpin Gel and PCR Clean-up Kit (Machery Nagel).
For amplification of the selection marker, the pUG7-HygB construct (
After transformation and recovery for 2 hours in YEPhD at 30° C. the cells were plated on YEPhD agar with 200 μg/ml HygB (Invitrogen). The plates were incubated at 30° C. for 2 days. Transformants were purified by re-streaking them on YEPhD agar with 200 μg/ml HygB. Correct integration and assembly was established with diagnostic PCR.
Example 9. Fermentation of STV058 and ALNQ 007_38000 and ALNQ 214_12000 Transporter Overexpression StrainsA pre-culture was inoculated with colony material from YEPh-D agar. The pre-culture was grown in 96-Half Deep Well Plate in 200 μl mineral medium with glucose as carbon source. The pre-culture was incubated 72 hours in an Infors incubator at 27° C., 750 rpm and 80% humidity.
40 μl of pre-culture was used to inoculate 2.5 ml mineral medium with glucose as carbon source in a 24-Deep Well Plate. These production cultures were incubated 120 hours in an Infors incubator at 27° C., 550 rpm, 80% humidity. The production cultures were well homogenized and 0.5 ml of culture was transferred to a 96-well plate. This sample was used as whole broth sample. The remainder of the production cultures were pelleted by centrifugation at 3000×g for 10 minutes. After centrifugation 0.5 supernatant was transferred to a 96-well plate. This sample was used as supernatant sample. Both the whole broth 96-well plates and supernatant 96-well plates were incubated for 10 minutes at 90° C. in a water bath and cooled down to room temperature. To each well 0.25 ml of acetonitrile was added and homogenized. The plates were then centrifuged at 3000×g for 10 minutes to pellet cell material and debris. The whole broth and supernatant samples were diluted 200 times in 33% acetonitrile. Samples were analyzed for RebA and other steviolglycosides using LC/MS. We found that the strains that had the particular transporter gene over-expressions as described, produced higher titers of Rebaudioside A or other steviolglycosides such as Rebaudioside B in the supernatant fraction compared to the parent strain. For an overview of the results, see Tables 12, 13.
Strains with over-expression of the ALNQ_007_38000 transporter or the ALNQ_214_12000 transporter have increased levels of Rebaudioside A in the supernatant. With the over-expression of the ALNQ_214_12000 transporter, the amount of RebA in the supernatant was increased with 5 to 6 fold compared to the reference strain. See also
Strains with over-expression of the ALNQ_007_38000 transporter or the ALNQ_214_12000 transporter have increased levels of Rebaudioside B in the supernatant. In the case of the ALNQ_007_38000 transporter this also results in a higher RebB concentration in the broth. See also
Strains with over-expression of the ALNQ_007_38000 transporter or the ALNQ_214_12000 transporter have decreased levels of Rebaudioside M in the broth. Because both transporters are efficient in exporting steviol glycosides such as Rebaudioside A and Rebaudioside B, lower amounts of these intermediates are available inside the cell for the conversion towards Rebaudioside M. Therefore, these transporters (or equivalent) may be target for deletion in a host that would have such a transporter, such as I. orientalis, to increase Rebaudioside M production.
Claims
1. A recombinant host capable of producing a steviol glycoside which overexpresses a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
2. A recombinant host capable of producing a steviol glycoside which has been modified, optionally in its genome, to result in a deficiency in the production of a polypeptide which mediates steviol glycoside transport and which polypeptide comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
3. The recombinant host according to claim 1, which comprises a recombinant nucleic acid encoding a polypeptide which comprises the amino acid sequence set forth in SEQ ID NO: 35 or SEQ ID NO: 38 or an amino acid sequence having at least about 50% sequence identity to either thereto.
4. The recombinant host according to claim 1, which further comprises one or more recombinant nucleotide sequence(s) encoding:
- a polypeptide having ent-copalyl pyrophosphate synthase activity;
- a polypeptide having ent-Kaurene synthase activity;
- a polypeptide having ent-Kaurene oxidase activity; and
- a polypeptide having kaurenoic acid 13-hydroxylase activity.
5. The recombinant host according to claim 1, which further comprises a recombinant nucleic acid sequence encoding a polypeptide having NADPH-cytochrome p450 reductase activity.
6. The recombinant host according to claim 1, which further comprises a recombinant nucleic acid sequence encoding one or more of:
- (i) a polypeptide having UGT74G1 activity;
- (ii) a polypeptide having UGT2 activity;
- (iii) a polypeptide having UGT85C2 activity; and
- (iv) a polypeptide having UGT76G1 activity.
7. The recombinant host according to claim 1, wherein the host belongs to one of the genera Saccharomyces, Aspergillus, Pichia, Kluyveromyces, Candida, Hansenula, Humicola, Issatchenkia, Trichosporon, Brettanomyces, Pachysolen, Yarrowia, Yamadazyma, or Escherichia.
8. The recombinant host according to claim 7, wherein the recombinant host is a Saccharomyces cerevisiae cell, a Yarrowia lipolitica cell, a Candida krusei cell, an Issatchenkia orientalis cell or an Escherichia coli cell.
9. The recombinant host according to claim 1, wherein the ability of the host to produce geranylgeranyl diphosphate (GGPP) is upregulated.
10. The recombinant host according to claim 1, which further comprises a nucleic acid sequence encoding one or more of:
- a polypeptide having hydroxymethylglutaryl-CoA reductase activity; or a polypeptide having farnesyl-pyrophosphate synthetase activity.
11. A recombinant host capable of producing a steviol glycoside which overexpresses a heterologous polypeptide which mediates steviol glycoside transport.
12. A process for the preparation of a steviol glycoside which comprises fermenting the recombinant host according to claim 1 in a suitable fermentation medium and, optionally, recovering the steviol glycoside.
13. The process according to claim 12 for the preparation of a steviol glycoside, wherein the process is carried out on an industrial scale.
14. A fermentation broth comprising a steviol glycoside obtainable by the process according to claim 12.
15. A steviol glycoside obtained by the process according to claim 12.
16. A composition obtainable by the process according to claim 12.
17. A foodstuff, feed or beverage which comprises the steviol glycoside according to claim 15.
Type: Application
Filed: Aug 15, 2016
Publication Date: Aug 16, 2018
Inventors: Viktor Marius BOER (Echt), Priscilla ZWARTJENS (Echt), Eric VAN DEN BERG (Echt)
Application Number: 15/751,526
