General sake yeasts (e.g., Kyokai no.7, K7) show high fermentation ability and low sporulation frequency. Former is related to stress-response defect due to the loss-of-function of MSN4 and RIM15. Later is mainly caused by low IME1 expression, leading to difficulty in breeding and genetic analysis. Sake yeast Hiroshima no.6 (H6), which had been applied for sake fermentation, has sporulation ability. However, its detailed properties have not been unveiled. Here we present that the fermentation ability of H6 is suitable for sake brewing, and the precursor of dimethyl trisulfide in sake from H6 is low. MSN4 but not RIM15 of H6 has the same mutation as K7. Our phylogenetic analysis indicated that H6 is closely related to the K7 group. Unlike K7, H6 showed normal sporulation frequency in a partially RIM15-dependent manner, and IME1 in H6 was expressed. H6 possesses excellent properties as a partner strain for breeding by crossing.
Keywords: Sake yeast; fermentation ability; off-flavor; phylogenetic analysis; sporulation.