Heterosis observed in Aspergillus oryzae and its significance in Koji manufacture.

Abstract

As is expected, a fast growing mutant on casein medium produced larger amount of protease than its parent or sister cultures. As a rule, the mutant yielded protease in a later stage of growth in contrast to its sister strain which produced it at an earlier stage. The heterocaryon between slow growing strains produced protease early as well as late, and the activity increased far beyond the productions limit of each component strain. Upon measuring the nuclear ratios during cultivation, the effect was considered to be due to heterocaryotic vigor or a kind of heterosis. The heterozygous diploid between slow growers also yielded protease as well as the heterocaryon. When fast grower and slow grower were paired, the resulting diploid showed the highest activity of the enzyme among these strains.