Method for obtaining low ethanol-producing yeast strains, yeast strains obtained therefrom and their use

Abstract

The present disclosure concerns a process for obtaining a variant yeast strain capable of producing less ethanol in an alcoholic fermentation process than its corresponding ancestral strain. The variant yeast strain is obtained by culturing the ancestral strain in the presence of increasing concentrations of a salt capable of causing an hyperosmotic stress to the ancestral yeast strain. The present disclosure also concerns variant yeast strain obtained from this process (for example the variant yeast strain deposited at Institut Pasteur, on Jan. 9, 2014, under accession number CNCM I-4832, the variant yeast strain deposited at Institut Pasteur, on Oct. 18, 2012 under accession number CNCM I-4684, the variant yeast strain deposited at Institut Pasteur, on Oct. 18, 2012 under accession number CNCM I-4685 and/or the variant yeast strain deposited at Institut Pasteur on Jan. 28, 2015 under accession number CNCM I-4952) as well as processes using the variant yeast strain (wine fermentation for example).

What is claimed is: 
     
         1 . A process for obtaining a variant yeast strain capable of producing, when compared to an ancestral yeast strain, more glycerol and less ethanol during an alcoholic fermentation process, said process comprising:
 a) culturing the ancestral yeast strain in a first culture medium comprising a salt capable of causing an hyperosmotic stress to the ancestral yeast strain, wherein the ancestral yeast strain is cultured in increasing salt concentrations and under conditions to achieve glucose depletion in the first culture medium so as to obtain a first cultured yeast strain; and   b) culturing the first cultured yeast strain in a second culture medium comprising the salt, wherein the first cultured yeast strain is cultured at a fixed salt concentration and under conditions to achieve glucose depletion in the second culture medium so as to obtain the variant yeast strain;   
       wherein
 the salt has a countercartion which is different than a sodium cation; and 
 the concentration of the salt in the second culture medium is higher than the concentration of the salt in the first culture medium. 
 
     
     
         2 . The process of  claim 1 , wherein the concentration of the salt in the first culture medium is between about 1.25 M and less than about 2.4 M and/or in the second culture medium is at least about 2.4 M. 
     
     
         3 . The process of  claim 1  or  2 , further comprising, at step a), increasing the salt concentration weekly or monthly. 
     
     
         4 . The process of any one of  claims 1  to  3 , wherein the first culture medium comprises glucose and the process further comprises, at step a), culturing the ancestral yeast strain in the first culture medium in decreasing glucose concentrations, wherein the concentration of glucose is preferably decreased weekly or monthly and wherein the concentration of glucose in the first culture medium is more preferably between about 14.0% and about 8.0% (w/v) with respect to the total volume of the first culture medium. 
     
     
         5 . The process of any one of  claims 1  to  4 , wherein the second culture medium comprises glucose and the process further comprises, at step b), culturing the first cultured yeast at a fixed glucose concentration and wherein the fixed glucose concentration of the second culture medium is preferably 8.0% (w/v) with respect to the total volume of the second culture medium. 
     
     
         6 . The process of any one of  claims 1  to  5 , further comprising mating haploid spores of the variant yeast strain to obtain a variant hybrid strain. 
     
     
         7 . The process of any one of  claims 1  to  6 , wherein the salt has a potassium countercation. 
     
     
         8 . The process of  claim 7 , wherein the salt is KCl. 
     
     
         9 . The process of any one of  claims 1  to  8 , wherein the variant yeast strain is from a  Saccharomyces  species and preferably from a genus selected from the group consisting of  Saccharomyces arboricolus, Saccharomyces eubayanus, Saccharomyces bayanus, Saccharomyces cerevisiae, Saccharomyces kudriadzevii, Saccharomyces mikatae, Saccharomyces paradoxus, Saccharomyces pastorianus, Saccharomyces carsbergensis, Saccharomyces uvarum  and inter-species hybrids. 
     
     
         10 . A variant yeast strain capable of producing, when compared to an ancestral yeast strain, more glycerol and less ethanol in an alcoholic fermentation process, said variant yeast being obtained by the process of any one of  claims 1  to  9 . 
     
     
         11 . The variant yeast strain of  claim 10  for making a fermented product, preferably wine and more preferably a red wine. 
     
     
         12 . A variant yeast strain deposited at Institut Pasteur, on Jan. 9, 2014, under accession number Collection Nationale des Cultures des Microorganismes (CNCM) I-4832. 
     
     
         13 . A variant yeast strain deposited at Institut Pasteur, on Oct. 18, 2012 under accession number Collection Nationale des Cultures des Microorganismes (CNCM) I-4684. 
     
     
         14 . A variant yeast strain deposited at Institut Pasteur, on Oct. 18, 2012 under accession number Collection Nationale des Cultures des Microorganismes (CNCM) I-4685. 
     
     
         15 . A variant yeast strain deposited at Institut Pasteur, on Jan. 28, 2015 under accession number Collection Nationale des Cultures des Microorganismes (CNCM) I-4952. 
     
     
         16 . A process for making a fermented product, said process comprising contacting the variant yeast strain of any one of  claims 10  to  15  with a fermentable source of nutrients. 
     
     
         17 . The process of  claim 16 , wherein the fermented produce is wine, preferably red wine, and the fermentable source of nutrients is a grape must.