Screening of asporogenic mutants of phytase-producing Aspergillus niger CFR 335 strain

Aspergillus niger is one of the fungi exploited industrially for the production of various metabolites including the
enzyme phytase. Intensive sporulation is a serious crisis in using this fungus, hence, in the present study an attempt was
made to obtain an asporulating strain.Materials and methods: A. niger CFR 335, a local phytase-producing isolate, was
induced to physical mutation by ultraviolet (UV) radiation and chemical mutation using different concentrations of ethyl
methane sulphonate (EMS) and N-methyl N?-nitro N-nitrosoguanidine (NTG).Results: UV exposure for 30 min, 10 mM
EMS and 25 mg ml1 of NTG were found to be optimum for maximum killing effect of 26.3%, 95% and 80% of the spores,
respectively. In this experiment, a stable auxotrophic mutant (ala) of A. niger CFR 335 with suppressed sporulation was
obtained. The auxotrophic mutant M-1 (A. niger CFR 335 ala) showed an improved specific activity of 1.26 U mg1 as
compared with the parent strain (0.85 U mg1).Conclusion: Sporulation was drastically reduced in the mutant M-1 without
affecting phytase yield, whereas the production rate was proportional to the rate of sporulation in the parent strain (A. niger
CFR 335).