INDUCTION OF ASPERGILLUS ORYZAE MUTANT STRAINS PRODUCING INCREASED LEVELS OF α-AMYLASE BY GAMMA-IRRADIATION

摘要

Some kind of fungi induces higher frequency of mutation by radiation compared with bacteria. In the case of Escherichia coli, mutation rate is below 0.1 % at 10~(-6) survivals (Kozabek et at., 1992). While, about 10-20% of mutation with color change of colony were observed on Aspergillus flavus at 10~(-4) survivals without severe increase or decrease of aflatoxin production (Ito et al., 1991). Many useful mutants of molds such as Aspergillus oryzae, A. niger, Penicillium notutum, etc. have been obtained by ultraviolet or X-rays irradiation for the improvement of fermentation process. However, some of conditions for the induction of mutation by ionizing radiation have not been elucidated well. In this paper, we present the data of gamma-rays irradiation on the mutation effect of Aspergillus oryzae with special reference to color changes of colonies and ability of enzyme productions.