Decreasing acetic acid accumulation by a glycerol overproducing strain of Saccharomyces cerevisiae by deleting the ALD6 aldehyde dehydrogenase gene

Abstract

Glycerol is a major fermentation product of Saccharomyces cerevisiae that contributes to the sensory character of wine. Diverting sugar to glycerol overproduction and away from ethanol production by overexpressing the glycerol 3-phosphate dehydrogenase gene, GPD2, caused S. cerevisiae to produce more than twice as much acetic acid as the wild-type strain (S288C background) in anaerobic cell culture. Deletion of the aldehyde dehydrogenase gene, ALD6, in wild-type and GPD2 overexpressing strains (GPD2-OP) decreased acetic acid production by three-and four-fold, respectively. In conjunction with reduced acetic acid production, the GPD2-OP ald6D strain produced more glycerol and less ethanol than the wild-type. The growth rate and fermentation rate were similar for the modified and wild-type strains, although the fermentation rate for the GPD2 ald6D strain was slightly less than that of the other strains from 24 h onwards. Analysis of the metabolome of the mutants revealed that genetic modification affected the production of some secondary metabolites of fermentation, including acids, esters, aldehydes and higher alcohols, many of which are flavour-active in wine. Modification of GPD2 and ALD6 expression represents an effective strategy to increase the glycerol and decrease the ethanol concentration during fermentation, and alters the chemical composition of the medium such that, potentially, novel flavour diversity is possible. The implications for the use of these modifications in commercial wine production require further investigation in wine yeast strains.

Cytosolic Redox Status of Wine Yeast (Saccharomyces Cerevisiae) under Hyperosmotic Stress during Icewine Fermentation

“…Our data supports other published work where the NADP + -dependent isoform Ald6p was identified as the main aldehyde dehydrogenase responsible for acetic acid production when sugar concentrations were at or below 200 g L −1 sugar [15,[19][20][21]. However, under high sugar conditions of 400 g L −1 , Erasmus et al linked acetic acid generation to NADPH production via Ald6p to compensate for the downregulation of genes in the pentose phosphate pathway [15], questioning the linkage of acetic acid production under osmotic stress to glycerol formation and NADH requirements.…”

Genetic Determinants of Volatile-Thiol Release bySaccharomyces cerevisiaeduring Wine Fermentation

“…A concurrent approach to genetic studies of wine aroma detection is a metabolomic footprinting approach that categorizes deletions based on the extracellular medium profile by liquid chromatography-MS (1,30) or GC-MS (13). Extracellular medium profiling is useful for wine aroma determination, as it is yeast metabolites which determine the aromas formed in a wine.…”

“…These aroma compounds can originate from distinct enzymatic reactions from well-characterized metabolic pathways in yeast and can be manipulated by expression of the enzymes involved, which in turn impacts the character of the resulting wine (13,24,29,32,33). However, many compounds of unknown biosynthetic origin arise during yeast fermentation (reviewed in references 5, 14, 22, and 29).…”

Progress in Metabolic Engineering of Saccharomyces cerevisiae

“…Cambon et al (41) combined (i) the overproduction of GPD (by overexpressing GPD1; see Fig. 2), the rate-controlling step in glycerol biosynthesis, with (ii) the deletion of ALD6, which was previously shown to result in lower acetate production in a laboratory yeast strain (79). In general, a major drawback of glycerol overproduction is the concomitant increase in other by-products of yeast metabolisms, particularly acetoin and acetaldehyde; these are undesirable in both beer and wine (223,239,290).…”