Intraspecific Hybridization by Protoplast Fusion in Mucorales Producing Milk-clotting Proteases

The properties of the intraspecific hybrids obtained by protoplast fusion of (+) and (–) mating type strains of Mucor pusillus producing the milk-clotting protease were studied, especially as to their mating types and enzyme productivities. All of the prototrophic hybrid strains obtained from the (+) ade/hyp + (–) cho fusion and three adenine-requiring segregants obtained on serial subcultivation formed zygospores autonomously. In the case of the (–)cho+(–) met fusion, most of the prototrophic hybrids had the (–) mating type, however, two of the 25 non-sectored hybrids were found to be homothallic and formed zygospores autonomously. Although the enzyme productivities of the intraspecific hybrids were lower than that of Mucor miehei, which is closely related to Mucor pusillus, the hybrids showed distinctly higher productivity than the parental Mucor pusillus strains.