Construction of bottom-fermenting yeasts that over express the ubiquitin ligase RSP5 gene and their effects on high-gravity fermentation

It has been reported that over expression of the ubiquitin ligase RSP5 gene conferred tolerance to various stresses in laboratory yeast Saccharomyces cereivisiae. We constructed strains of bottom-fermenting yeast, natural hybrid, in which the S. cerevisiae(SC)-RSP5 or Saccharomyces bayanus (SB)-RSP5 is highly expressed and used for high-gravity fermentation. The SB-RSP5-overexpressing yeast showed a higher fermentation rate than the parent strain. In contrast, the fermentation rate of the SC-RSP5-overexpressing yeast was slower than the parent strain. These results suggest significant functional differences in brewing between the SC-RSP5 and SB-RSP5 genes.