Introduction of flocculation into industrial yeast, Saccharomyces cerevisiae saké, by protoplast fusion.

Protoplast fusion was applied to obtain intraspecific fusion in yeast strains in order to overcome restrictions imposed by the natural mating system. Acriflavine was used to construct petite mutants from non-flocculent industrial Saccharomyces cerevisiae saké strain. UV radiation was used to construct ura- mutants from a respiratory competent and highly flocculent S. cerevisiae NCYC869 strain. Fusion products were selected by complementation on minimal medium. The frequency of appearance of prototrophic hybrids was five per 10(5) protoplasts. The stable hybrids showed not only the S. cerevisiae saké characteristics but also flocculation ability, thereby confirming the success of the fusion.