Identification of new Saccharomyces cerevisiae variants of the MET2 and SKP2 genes controlling the sulfur assimilation pathway and the production of undesirable sulfur compounds during alcoholic fermentation.

Isabelle Sanchez,Bruno Blondin,Jessica Noble

doi:10.1186/s12934-015-0245-1

Isabelle Sanchez, Bruno Blondin + Show 1 more

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https://doi.org/10.1186/s12934-015-0245-1

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Abstract

BackgroundWine yeasts can produce undesirable sulfur compounds during alcoholic fermentation, such as SO2 and H2S, in variable amounts depending mostly on the yeast strain but also on the conditions. However, although sulfur metabolism has been widely studied, some of the genetic determinants of differences in sulfite and/or sulfide production between wine yeast strains remain to be identified. In this study, we used an integrated approach to decipher the genetic determinants of variation in the production of undesirable sulfur compounds.ResultsWe examined the kinetics of SO2 production by two parental strains, one high and one low sulfite producer. These strains displayed similar production profiles but only the high-sulfite producer strain continued to produce SO2 in the stationary phase. Transcriptomic analysis revealed that the low-sulfite producer strain overexpressed genes of the sulfur assimilation pathway, which is the mark of a lower flux through the pathway consistent with a lower intracellular concentration in cysteine. A QTL mapping strategy then enabled us to identify MET2 and SKP2 as the genes responsible for these phenotypic differences between strains and we identified new variants of these genes in the low-sulfite producer strain. MET2 influences the availability of a metabolic intermediate, O-acetylhomoserine, whereas SKP2 affects the activity of a key enzyme of the sulfur assimilation branch of the pathway, the APS kinase, encoded by MET14. Furthermore, these genes also affected the production of propanol and acetaldehyde. These pleiotropic effects are probably linked to the influence of these genes on interconnected pathways and to the chemical reactivity of sulfite with other metabolites.ConclusionsThis study provides new insight into the regulation of sulfur metabolism in wine yeasts and identifies variants of MET2 and SKP2 genes, that control the activity of both branches of the sulfur amino acid synthesis pathway and modulate sulfite/sulfide production and other related phenotypes. These results provide novel targets for the improvement of wine yeast strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0245-1) contains supplementary material, which is available to authorized users.

Highlights

Wine yeasts can produce undesirable sulfur compounds during alcoholic fermentation, such as SO2 and H2S, in variable amounts depending mostly on the yeast strain and on the conditions
Characterization of sulfite production during alcoholic fermentation We selected two Saccharomyces cerevisiae strains, both of which were homozygous diploid derivatives of wine yeasts, which were previously shown to differ in their ability to produce sulfite: JN10, a high sulfite-producing strain, and JN17, a low sulfite-producing strain
After a similar lag phase, the maximum rate of CO2 production was higher for the JN10 strain than for the JN17 strain, the JN17 strain maintained a slightly higher rate of CO2 release during the beginning of the stationary phase

Summary

Introduction

Wine yeasts can produce undesirable sulfur compounds during alcoholic fermentation, such as SO2 and H2S, in variable amounts depending mostly on the yeast strain and on the conditions. The excessive production of H2S can lead to off-flavors [1,2] and a high concentration of sulfites can delay the onset of malolactic fermentation by inhibiting lactic acid bacteria [3,4] and is a source of health concerns. Given their toxicity, the final concentration of sulfites in wine is regulated by law. The production of sulfites and sulfide by wine yeasts are highly strain-dependent, and despite strong selective processes some commercial yeast still produce high amounts of these sulfur compounds in some circumstances. The identification of genes involved in such variations between strains will enable the optimization of the fermentation process and the construction of strains that produce low amounts of negative sulfur metabolites through breeding strategies

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