Breeding bafilomycin A1-resistant sake yeast to improve fermentative capacity

Sake yeast exhibits remarkable fermentative capacity in mash environments, even under various stress conditions. Although breeding techniques aimed at improving the flavor of sake by modifying aroma compounds and organic acid composition have been employed, these approaches often result in reduced fermentative capacity. Furthermore, existing breeding methods aimed at enhancing fermentative capacity often result in increased acidity in the final product. In this study, we aimed to improve sake yeast fermentative capacity while limiting sake acidity. Depletion of intracellular ATP may enhance fermentative capacity, suggesting that strains with high vacuolar-type ATPase (V-ATPase) activity exhibit improved fermentative capacity. Thus, we subjected sake yeast to ultraviolet mutagenesis and bafilomycin A1 (Baf), a V-ATPase inhibitor, to select resistant strains. The selected Baf-resistant strains exhibited no changes in growth rate, cell morphology, or vacuolar morphology compared to the parent strain. However, increased vacuolar acidity and decreased intracellular ATP levels indicated enhanced V-ATPase activity. Moreover, evaluation of brewing characteristics confirmed improved fermentative capacity without increases in acidity or amino acid content. The results of this study suggest that obtaining a Baf-resistant strain can reduce intracellular ATP levels, thereby increasing fermentative capacity without increasing acidity.