Locus heterogeneity in the mechanism underlying the superior fermentation performances of phylogenetically distant sake yeasts.

Sake yeasts, Saccharomyces cerevisiae strains isolated from Japanese sake fermentation tanks, exhibit superior fermentation performance to that of other yeast strains. Although the exceptional abilities of the modern sake yeast strain K701 have been extensively investigated, those of phylogenetically distant classical sake yeasts remain largely understudied. In this study, we aimed to clarify the mechanism underlying the superior fermentation ability of the classical sake yeast strain Km67 by comparing its genetic and physiological properties with those of the laboratory strains X2180 and K701. Km67 did not exhibit quiescence-specific phenotypes in sake mashes in the same manner as K701. RNA sequencing revealed similar trends between the transcriptomes of Km67 and K701 in sake mash, suggesting that the lack of quiescence entry was related to the higher fermentation ability of Km67. Genetic testing demonstrated that signals upstream of Rim15p were not conveyed downstream, indicating impaired fermentation repression mediated by Rim15p in Km67 cells. Protein phosphatase 2A (PP2A) activity declined following CDC55 deletion downstream of Rim15p, consequently reducing the fermentation performance of Km67. However, the extent of fermentation reduction upon CDC55 deletion was not as large as that with X2180 and K701. This suggested the presence of unidentified factors that regulated fermentation independently of PP2A or Rim15p in Km67. Thus, our findings demonstrate locus heterogeneity in the mechanism underlying fermentation abilities between the phylogenetically distant sake yeasts Km67 and K701.