Over-expression of gds1 in yeast for increased ethanol and decreased acetate production

Abstract

Described are compositions and methods relating to modified yeast that over-express the glycerol-deficient suppressor, GDS1. The yeast produces an increased amount of ethanol and a deceased amount of acetate compared to parental cells. Such yeast is particularly useful for large-scale ethanol production from starch substrates where acetate in an undesirable end product.

What is claimed is: 
     
         1 . Modified yeast cells derived from parental yeast cells, the modified cells comprising a genetic alteration that causes the modified cells to produce an increased amount of GDS1 polypeptides compared to the parental cells, wherein the modified cells produce during fermentation a decreased amount of acetate compared to the amount of acetate produced by the parental cells under identical fermentation conditions. 
     
     
         2 . The modified yeast cells of  claim 1 , wherein the modified cells produce during fermentation an increased amount of ethanol compared to the amount of ethanol produced by the parental cells under identical fermentation conditions. 
     
     
         3 . The modified cells of  claim 1  or  2 , wherein the genetic alteration comprises the introduction into the parental cells of a nucleic acid capable of directing the expression of a GDS1 polypeptide to a level above that of the parental cell grown under equivalent conditions. 
     
     
         4 . The modified cells of  claim 1  or  2 , wherein the genetic alteration comprises the introduction of an expression cassette for expressing a GDS1 polypeptide. 
     
     
         5 . The modified cells of any of  claims 1 - 5 , wherein the cells further comprising one or more genes of the phosphoketolase pathway. 
     
     
         6 . The modified cells of  claim 5 , wherein the genes of the phosphoketolase pathway are selected from the group consisting of phosphoketolase, phosphotransacetylase and acetylating acetyl dehydrogenase. 
     
     
         7 . The modified cells of any of  claims 1 - 6 , wherein the amount of increase in the expression of the GDS1 polypeptide is at least about 500% compared to the level expression in the parental cells grown under equivalent conditions. 
     
     
         8 . The modified cells of any of  claims 1 - 6 , wherein the amount of increase in the production of mRNA encoding the GDS1 polypeptide is at least about 1000% compared to the level in the parental cells grown under equivalent conditions. 
     
     
         9 . The modified cells of any of  claims 1 - 6 , wherein the amount of increase in the production of mRNA encoding the GDS1 polypeptide is at least about 5000% compared to the level in the parental cells grown under equivalent conditions. 
     
     
         10 . The modified cells of any of  claims 1 - 6 , wherein the amount of increase in the production of mRNA encoding the GDS1 polypeptide is at least about 10000% compared to the level in the parental cells grown under equivalent conditions. 
     
     
         11 . The modified cells of any of  claims 1 - 10 , wherein the cells further comprise an exogenous gene encoding a carbohydrate processing enzyme. 
     
     
         12 . The modified cells of any of  claims 1 - 11 , further comprising an alteration in the glycerol pathway and/or the acetyl-CoA pathway. 
     
     
         13 . The modified cells of any of  claims 1 - 12 , further comprising an alternative pathway for making ethanol. 
     
     
         14 . The modified cells of any of  claims 1 - 13 , wherein the cells are of a  Saccharomyces  spp. 
     
     
         15 . A method for decreasing the production of acetate from yeast cells grown on a carbohydrate substrate, comprising: introducing into parental yeast cells a genetic alteration that increases the production of GDS1 polypeptides compared to the amount produced in the parental cells. 
     
     
         16 . A method for increasing the production of ethanol from yeast cells grown on a carbohydrate substrate, comprising: introducing into parental yeast cells a genetic alteration that increases the production of GDS1 polypeptides compared to the amount produced in the parental cells. 
     
     
         17 . The method of  claim 15  or  16 , wherein the cells having the introduced genetic alteration are the modified cells are the cells of any of  claims 1 - 15 . 
     
     
         18 . The method of  claim 15  or  17 , wherein the decrease in acetate production is at least 10%, at least 15%, at least 20%, or at least 25%. or at least 30% compared to the amount produced in the parental cells. 
     
     
         19 . The method of  claim 16  or  17 , wherein the increase in ethanol production is at least 0.1%, at least 0.2%, at least 0.3%, or at least 0.5%. or at least 1.0% compared to the amount produced in the parental cells. 
     
     
         20 . The method of any of  claims 15 - 19 , wherein GDS1 polypeptides are over-expressed by at least 500%. 
     
     
         21 . The method of any of  claims 15 - 19 , wherein GDS1 polypeptides are over-expressed by at least 5-fold. 
     
     
         22 . The method of any of  claims 15 - 19 , wherein GDS1 polypeptides are over-expressed by at least 10-fold. 
     
     
         23 . The method of any of  claims 15 - 19 , wherein GDS1 polypeptides are over-expressed by at least 50-fold. 
     
     
         24 . The method of any of  claims 15 - 19 , wherein GDS1 polypeptides are over-expressed by at least 100-fold.