Efficient Production of Steviol Glycosides in Recombinant Hosts

Abstract

Recombinant microorganisms are disclosed that produce steviol glycosides and have altered expression of one or more endogenous transporter or transcription factor genes, or that overexpress one or more heterologous transporters, leading to increased excretion of steviol glycosides of interest.

1 . A recombinant microorganism capable of producing a steviol glycoside in a cell culture,
 wherein the microorganism has a modified expression of at least one endogenous transporter gene and at least one endogenous transcription factor gene that regulates expression of the at least one endogenous transporter gene,   wherein the modified expression comprises reduced expression or activity of the at least one endogenous transporter gene, having at least 80% sequence identity to the amino acid sequence set forth in SEQ ID NO:113;   wherein the reduced expression is produced in the microorganism by disrupting or deleting the gene locus for the at least one endogenous transporter gene;   wherein the microorganism further expresses at least one heterologous transporter gene;   wherein the steviol glycoside is Rebaudioside A, Rebaudioside B, Rebaudioside D, Rebaudioside E, Rebaudioside M, or an isomer thereof.   
     
     
         2 . The recombinant microorganism of  claim 1 , wherein the endogenous and/or the heterologous transporter gene encodes an ATP-Binding Cassette (ABC) transporter. 
     
     
         3 . The recombinant microorganism of  claim 1 , wherein the heterologous transporter gene is a  Stevia  transporter gene. 
     
     
         4 . The recombinant microorganism of  claim 1 , further comprising a gene encoding a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; wherein the gene has a copy number of 2 or more; and wherein the polypeptide comprises a polypeptide having at least 90% sequence identity to one of the amino acid sequences set forth in any one of SEQ ID NOs:51, 54, 55, 86, or 90. 
     
     
         5 . The recombinant microorganism of  claim 4 , wherein the gene is codon optimized for expression in the microorganism. 
     
     
         6 . The recombinant microorganism of  claim 5 , wherein the gene is codon optimized for expression in  Saccharomyces cerevisiae.    
     
     
         7 . The recombinant microorganism of  claim 1 , wherein the recombinant microorganism is a yeast cell from  Saccharomyces.    
     
     
         8 . A method of affecting excretion of a steviol glycoside from a cell culture, comprising culturing the recombinant microorganism of  claim 1  under conditions in which the genes are expressed;
 wherein the steviol glycoside is produced by the recombinant microorganism. 
 
     
     
         9 . A method of producing a steviol glycoside in a cell culture, comprising culturing the recombinant microorganism of  claim 1  under conditions in which the at least one endogenous transporter gene, the at least one endogenous transcription factor gene that regulates expression of the at least one endogenous transporter gene, or both are expressed; wherein the steviol glycoside is produced by the recombinant microorganism. 
     
     
         10 . The method of  claim 9 , wherein culturing includes inducing expression of the at least one endogenous transporter gene, the at least one endogenous transcription factor gene that regulates expression of the at least one endogenous transporter gene, or both. 
     
     
         11 . The method of  claim 9 , wherein culturing includes constitutively expressing the at least one endogenous transporter gene, the at least one endogenous transcription factor gene that regulates expression of the at least one endogenous transporter gene, or both. 
     
     
         12 . The method of  claim 9 , wherein:
 (a) Rebaudioside A is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-13 hydroxyl group; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside;   (b) Rebaudioside B is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-13 hydroxyl group; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; and polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside;   (c) Rebaudioside D is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylating steviol or the steviol glycoside at its C-13 hydroxyl group; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside;   (d) Rebaudioside E is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-13 hydroxyl group; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; and/or   (e) Rebaudioside M is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylation of the 13-OH of steviol; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside.   
     
     
         13 . The method of  claim 9 , wherein Rebaudioside A is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-13 hydroxyl group; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-0-glucose of a steviol glycoside; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside. 
     
     
         14 . The method of  claim 9 , wherein Rebaudioside D is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylating steviol or the steviol glycoside at its C-13 hydroxyl group; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-0-glucose of a steviol glycoside; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside. 
     
     
         15 . The method of  claim 10 , wherein Rebaudioside M is synthesized in the recombinant microorganism expressing a polypeptide capable of glycosylation of the 13-OH of steviol; a polypeptide capable of beta 1,3 glycosylation of the C3′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside; a polypeptide capable of glycosylating steviol or a steviol glycoside at its C-19 carboxyl group; and a polypeptide capable of beta 1,2 glycosylation of the C2′ of the 13-O-glucose, 19-O-glucose, or both 13-O-glucose and 19-O-glucose of a steviol glycoside. 
     
     
         16 . The method of  claim 9 , wherein steviol glycoside is produced at a concentration of at least 500 mg/L of cell culture. 
     
     
         17 . The method of  claim 15 , that further comprises isolating the Rebaudioside M, alone or together with at least one other steviol glycoside from the cell culture. 
     
     
         18 . The method of  claim 17 , wherein the isolating step comprises separating a liquid phase of the cell culture from a solid phase of the cell culture to obtain a supernatant comprising Rebaudioside M, alone or together with at least one other steviol glycoside, and:
 (a) contacting the supernatant with one or more adsorbent resins in order to obtain at least a portion of Rebaudioside M, alone or together with at least one other steviol glycoside; or   (b) contacting the supernatant with one or more ion exchange or reversed-phase chromatography columns in order to obtain at least a portion of Rebaudioside M, alone or together with at least one other steviol glycoside; or   (c) crystallizing or extracting Rebaudioside M, alone or together with at least one other steviol glycoside;   thereby isolating Rebaudioside M, alone or together with at least one other steviol glycoside.   
     
     
         19 . The method of  claim 9 , that further comprises recovering a steviol glycoside composition comprising Rebaudioside M, alone or together with at least one other steviol glycoside from the cell culture. 
     
     
         20 . The method of  claim 19 , wherein the recovered steviol glycoside composition is enriched for Rebaudioside M relative to a steviol glycoside composition of  Stevia  plant and has a reduced level of  Stevia  plant-derived components relative to a steviol glycoside composition obtained from a plant-derived  Stevia  extract. 
     
     
         21 . The method of  claim 9 , wherein the recombinant microorganism is grown in a fermentor at a temperature for a period of time, wherein the temperature and the period of time facilitate the production of the steviol glycoside composition. 
     
     
         22 . A cell culture, comprising the recombinant microorganism of  claim 1 , the cell culture further comprising:
 (a) the steviol glycoside produced by the recombinant microorganism;   (b) glucose, fructose, sucrose, xylose, rhamnose, uridine diphosphate (UDP)-glucose, UDP-rhamnose, UDP-xylose, and/or N-acetyl-glucosamine; and   (c) supplemental nutrients comprising trace metals, vitamins, salts, YNB, and/or amino acids;   wherein the steviol glycoside is present at a concentration of at least 1 mg/liter of the cell culture.   
     
     
         23 . The recombinant microorganism of  claim 1 , wherein the recombinant microorganism is a plant cell, a mammalian cell, an insect cell, a fungal cell from  Aspergillus  genus, or a yeast cell from  Saccharomyces cerevisiae, Schizosaccharomyces pombe, Yarrowia lipolytica, Candida glabrata, Ashbya gossypii, Cyberlindnera jadinii, Pichia pastoris, Kluyveromyces lactis, Hansenula polymorpha, Candida boidinii, Arxula adeninivorans, Xanthophyllomyces dendrorhous , or  Candida albicans  species, an algal cell or a bacterial cell from  Escherichia coli  species, or  Bacillus  genus. 
     
     
         24 . A steviol glycoside produced by the recombinant microorganism of  claim 1 . 
     
     
         25 . A sweetener composition, comprising the steviol glycoside of  claim 24 . 
     
     
         26 . A food product, comprising the sweetener composition of  claim 25 . 
     
     
         27 . A beverage or a beverage concentrate, comprising the sweetener composition of  claim 25 .