Saccharomyces strain variability in hydrogen sulfide formation under enological conditions.

摘要

Hydrogen sulfide is an undesirable by-product of alcoholic fermentation by yeast and one of the major problems in the wine and beer industries. The main reason this compound is a principle sensory defect of wine and beer is the low concentration required for its aroma threshold to be reached, compared to other volatile substances.; Hydrogen sulfide production was investigated in twenty-nine strains of Saccharomyces cerevisiae, two commercial strains and twenty-seven natural isolates. Hydrogen sulfide was evaluated in a number of different media, including grape juice and two synthetic media simulating grape juice. From this analysis several strains were identified that displayed differences in hydrogen sulfide formation in response to changing medium composition.; Proteome analysis was run comparing protein profiles of two commercial yeast strains exhibiting the highest difference in hydrogen sulfide formation and two laboratory strains. All four strains were grown in laboratory media and the two wine isolates in synthetic grape juice media at two different nitrogen levels. Possible candidates for thirteen proteins corresponding to products of structural genes with known functions in the sulfate reduction pathway as well as in the biosynthesis of sulfur containing compounds were identified on the two dimensional gels. In addition a number of unique spots to each condition were resolved. Thirty-seven unique protein spots were resolved for UCD522 in the lower nitrogen level and thirty-nine in the high. For UCD713 thirty-seven protein spots were resolved in the low nitrogen level and forty-one in the high. Several protein spots representing strain or media growth conditions were also identified in this study. Determination of the identity of these proteins would also provide insight into strain variability and nitrogen metabolism.; In addition the impact of over expressing MET17 on hydrogen sulfide production was evaluated in these two strains, in both high and low nitrogen levels. Over-expression of MET17 resulted in a 10 to 70-fold increase in O-acetylserine/O-acetylhomoserine sulfhydrylase (OAS/OAH SHLase) activity in UCD522 but had no impact on the level of H₂S produced. In contrast OAS/OAH SHLase was not highly over-expressed in transformants of UCD713 (0.5 to 10-fold) but resulted in greatly reduced H₂S formation.