The completion of the sequence of the genome of the yeast Saccharomyces allowed identification of every gene in this organism. Mutations of each gene have been constructed and the entire set of mutations is available for analysis. The aim of this project is to identify every mutation that results in sulfide formation in wine yeast and those that suppress it. If the mutations suppressing sulfide formation could be identified, the altered alleles of the genes involved could be transferred to other genetic backgrounds resulting in commercial strains with reduced ability to produce hydrogen sulfide during wine production. The goal of this study was to identify genes leading to reduced sulfide formation and to confirm the role of those genes in sulfide formation in genetic crosses.
This study has focused on strain UCD932. This strain is a low sulfide producer under all conditions evaluated. We discovered that this strain carries two independent mutations affecting sulfide production. One leads to reduced production of sulfide and the other to increased consumption of reduced sulfide. The additive effect of these genes is to keep sulfide levels low in the cell. Over-expression of these modified alleles did not result in sulfide reduction in high sulfide-producing strains indicating that these altered alleles are not dominant in the presence of a wild type copy of the gene. Genetic crossing against high sulfide producers indicated that both genes could reduce sulfide formation to some extent with the greatest reduction occurring when both were present simultaneously. Thus this project has been successful and the goals of the research have been met. The next phase of this work will be the use of these altered alleles in the genetic modification of commercial strains. This will allow us to develop strains with reduced sulfide formation potential to meet the overall aim of my laboratory ?which is the elimination of sulfide production by yeast as a cause of hydrogen sulfide during wine production.