HETEROTHALLISM IN SACCHAROMYCES ROUXII

Abstract

S. rouxii is the principal yeast found in miso, the fermented Japanese food produced from soybeans. This yeast is heterothallic, yet each sex may self diploidize to a limited extent, the conjugated cells immediately forming asci. S. rouxii normally produces glistening colonies and no pellicles on liquid media. Such isolates are more strongly fermentative than the less common mat colony type which forms pellicles. Opposite sexes of the glistening type mate readily. The intensity of the mating reaction is heightened by a sexual agglutination mechanism that causes asci to occur in clusters so large they can be seen by the unaided eye. Sodium chloride in 10% concentration stimulates sporulation markedly. Sexual reactions between glistening isolates of opposite sex are strong; between mat and glistening isolates the sexual reactions are weak, and between mat isolates sexual reactions are almost nil. The mat isolates have a strong tendency to form diploid vegetative cells following self diploidization. The diploids produce aborted ascospores exclusively.