Screening of asporogenic mutants of phytase-producingAspergillus nigerCFR 335 strain

Abstract

Objective: 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 ug ml^-1 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 mg^-1 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). Key words: asporulation, Aspergillus niger CFR 335, phytase, ethyl methane sulphonate, N- methyl N?-nitro N-nitrosoguanidine, ultraviolet radiation