Interspecific hybrids between
Aspergillus oryzae wigh high acid carboxypeptidase productivity and
Aspergillus sojae with low α-amylase productivity were obtained through protoplast fusion. A stable diploid strain, which seems to be excellent in making
koji for
shoyu (soy sauce) production, was obtained from a fusant by successive subcultures. A haploid strain S 360 was obtained from the diploid treated with benomyl. The α-amylase productivity of strain S 360 was lower than that of the parental strain of
A. oryzae. On the other hand, the acid carboxypeptidase productivity of the former was nearly equal to that of the latter. Morphological characters of the conidial wall and conidiophore wall of
A. oryzae were inherited in the strain S 360, whose physiological characters of α-amylase and kojic acid productivities were intermediate between
A. oryzae and
A. sojae. Strain S 360 was genetically highly stable, bore abundant conidia in wheat bran
koji, and had high productivity of acid carboxypeptidase and low α-amylase productivity in a
shoyu koji culture. Thus the haploid strain S 360 seems to be an improved strain in the practical point of view such as enzyme activities, numbers of conidia of wheat bran
koji etc.
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