Affiliation:
1. Department of Viticulture and Enology, University of California, Davis, Davis, California 95616-8749
Abstract
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 low-nitrogen 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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
57 articles.
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