UC Davis

In order to better understand their impact on ethanol tolerance in Saccharomyces cerevisiae, six individual genes were overexpressed in two different commercial wine yeast strains, Montrachet and Elixir, and fermented in a high brix, defined, wine-like medium. These genes mainly consisted of those involved in the production of unsaturated fatty acids, although genes dealing with glycerol efflux and reactive oxygen species sequestration were also evaluated. The fermentations were monitored for brix, biomass, and nitrogen utilization. HPLC analysis of hexose sugars, glycerol, and ethanol was reserved for the most interesting of these genes, FPS1 and FAS1, in order to further understand the metabolism associated with these genetic changes. A final fermentation was then run using mutants lacking the FPS1 gene, and mutants overexpressing both components of the FAS complex, FAS1 and FAS2. The results showed a clear trend of greater ethanol tolerance, measured as the amount of ethanol produced before the cessation of fermentation, with less expression of FPS1 in Montrachet, but little result in Elixir. The FPS1 deletion mutant for the Montrachet strain developed higher biomass, utilized more sugar, and produced more ethanol compared to the control. Likewise, overexpression of the FAS complex showed a deleterious effect on the same ethanol tolerance proxies of Elixir, with more muted results in Montrachet. FAS overexpression caused reduced biomass and more sluggish fermentation. These responses demonstrate not only the potential of leveraging these genes for the production of novel commercial strains of S. cerevisiae, but also the interesting strain dependent responses associated with their differential expression.