Glycerol Overproduction by EngineeredSaccharomyces cerevisiaeWine Yeast Strains Leads to Substantial Changes in By-Product Formation and to a Stimulation of Fermentation Rate in Stationary Phase

Abstract

Six commercial wine yeast strains and three nonindustrial strains (two laboratory strains and one haploid strain derived from a wine yeast strain) were engineered to produce large amounts of glycerol with a lower ethanol yield. Overexpression of the GPD1 gene, encoding a glycerol-3-phosphate dehydrogenase, resulted in a 1.5- to 2.5-fold increase in glycerol production and a slight decrease in ethanol formation under conditions simulating wine fermentation. All the strains overexpressing GPD1 produced a larger amount of succinate and acetate, with marked differences in the level of these compounds between industrial and nonindustrial engineered strains. Acetoin and 2,3-butanediol formation was enhanced with significant variation between strains and in relation to the level of glycerol produced. Wine strains overproducing glycerol at moderate levels (12 to 18 g/liter) reduced acetoin almost completely to 2,3-butanediol. A lower biomass concentration was attained byGPD1-overexpressing strains, probably due to high acetaldehyde production during the growth phase. Despite the reduction in cell numbers, complete sugar exhaustion was achieved during fermentation in a sugar-rich medium. Surprisingly, the engineered wine yeast strains exhibited a significant increase in the fermentation rate in the stationary phase, which reduced the time of fermentation.

The glutamate synthase (GOGAT) of plays an important role in central nitrogen metabolism

“…We did not detect di¡erences in the acetate concentration between the wildtype and the mutant and succinate was a bit higher in the wild-type. A lower biomass concentration was also reported by GPD1-overexpressing strains, probably because acetaldehyde production increased during the growth phase [37]. However, our cultures were limited in glutamine and the yield was determined by the nitrogen content in the feed.…”

Upregulation ofALD3andGPD1inSaccharomyces cerevisiaeduring Icewine fermentation

“…Wine yeast display properties which are distinct from laboratory strains of Saccharomyces cerevisiae and these differences can impact the organoleptic properties of the finished wine (Bidenne et al 1992;Remize et al 1999;Hauser et al 2001). Analysis of the initial hyperosmotic stress response of wine yeast to fermentable sugars found an isoform of pyruvate decarboxylase (PDC6), a key enzyme in fermentative metabolism, upregulated in the wine yeast (Erasmus et al 2003) but this gene was not upregulated in laboratory yeast strains exposed to salt or sorbitol stress (Rep et al 2000).…”

Genetic and enological analysis of selected Saccharomyces cerevisiae strains for wine production

“…Besides contributing to the increased sweetness of wine, the overproduction of glycerol at the expense of ethanol had been investigated as a means to produce wines with low ethanol levels without altering their organoleptic properties. The relative efficiency of glycerol-3-phosphate dehydrogenase and alcohol dehydrogenase for NADH 2 that mediates the metabolic pathways of both ethanol and glycerol production allows the glycerol-ethanol ratios to be varied from 1 ⁄ 10 to 1 ⁄ 15 (Remize et al, 1999). The glycerol-ethanol ratios for the 26108 and 96581 strains correspond to 1 ⁄ 14.6 and 1 ⁄ 12.4, respectively, compared with the ratios of the wine yeasts in the range of 1 ⁄ 14.1-1 ⁄ 16.5.…”