MET17and Hydrogen Sulfide Formation inSaccharomyces cerevisiae

Abstract

Commercial isolates of Saccharomyces cerevisiae differ in the production of hydrogen sulfide (H 2 S) during fermentation, which has been attributed to variation in the ability to incorporate reduced sulfur into organic compounds. We transformed two commercial strains (UCD522 and UCD713) with a plasmid overexpressing the MET17 gene, which encodes the bifunctional O-acetylserine/O-acetylhomoserine sulfhydrylase (OAS/OAH SHLase), to test the hypothesis that the level of activity of this enzyme limits reduced sulfur incorporation, leading to H 2 S release. Overexpression of MET17 resulted in a 10-to 70-fold increase in OAS/OAH SHLase activity in UCD522 but had no impact on the level of H 2 S produced. In contrast, OAS/OAH SHLase activity was not as highly expressed in transformants of UCD713 (0.5-to 10-fold) but resulted in greatly reduced H 2 S formation. Overexpression of OAS/OAH SHLase activity was greater in UCD713 when grown under lownitrogen conditions, but the impact on reduction of H 2 S was greater under high-nitrogen conditions. Thus, there was not a good correlation between the level of enzyme activity and H 2 S production. We measured cellular levels of cysteine to determine the impact of overexpression of OAS/OAH SHLase activity on sulfur incorporation. While Met17p activity was not correlated with increased cysteine production, conditions that led to elevated cytoplasmic levels of cysteine also reduced H 2 S formation. Our data do not support the simple hypothesis that variation in OAS/OAH SHLase activity is correlated with H 2 S production and release.

Origins of Grape and Wine Aroma. Part 1. Chemical Components and Viticultural Impacts

“…That is because these sources of nitrogen are precursors for O-acetylserine or O-acetylhomoserine synthesis, which are important in the synthesis of cysteine, methionine, and glutathione (Giudici and Kunkee 1994, Jiranek et al 1995, Linderholm et al 2008. The activity of Oacetylserine/O-acetylhomoserine sulfhydrylase (the enzyme responsible for incorporating reduced sulfur into organic compounds) is not the only factor important for reducing H 2 S production, but rather the activity of a complement of enzymes involved in the synthesis of O-acetyl-L-homoserine and homocysteine can help to reduce H 2 S production in S. cerevisiae (Spiropoulos andBisson 2000, Linderholm et al 2008). Interestingly, a recent study indicates that the nutrients used during rehydration of yeasts for use in grape juice fermentations can influence formation of H 2 S (and other volatiles) (Winter et al 2011).…”

The Microbiology of Malting and Brewing

“…The production of SO 2 and hydrogen sulfide is linked a priori, through reduction of the former by sulfite reductase (148). However, it is possible to regulate their levels independently (149).…”

Lactic Acid Bacteria as a Potential Source of Enzymes for Use in Vinification

“…The bulk of the nitrogenous fraction is comprised of the alpha amino acids and ammonium (25,126), which along with peptides containing up to five amino acid residues (16,199) represent the assimilable nitrogen that is vital for yeast growth and fermentative activity (30,139,191,238) and suppression of hydrogen sulfide (100,112,138,263). Conversely, the proteins of grapes are considered a nuisance as they become unstable in the finished wine and can precipitate to produce a haze (15,133,290).…”