Improvement of alkaline protease production by Penicillium chrysogenum NRRL 792 through physical and chemical mutation, optimization, characterization and genetic variation between mutant and wild-type strains

Abstract

Penicillium chrysogenum NRRL 792 was exposed successively to gamma radiation (physical mutagen) and ethyl methansulfonate (EMS; chemical mutagen). Gamma mutant G9 produced more alkaline protease than the wild type (62.92 vs. 40.0 U/g, respectively). Subsequent mutagenesis of G9 by EMS resulted in mutant EMS-1, which produced the highest level of enzyme (120.0 U/g). Optimal conditions for alkaline protease production by this mutant fungal strain were examined. The optimized medium was supplemented with 1 % (w/w) casein and 2.5 mM MgSO4, while the optimal pH and temperature were 9, and 30 °C after 7 days of incubation. The purified mutant alkaline protease from EMS-1 was more stable than that from the wild-type, resulting in the former having a higher pH stability and thermostability. The mutant and wild enzymes were subjected to sodium dodecylsulfate-polyacrylamide gel electrophoresis. The purified mutant enzyme showed two bands with molecular weights of 40 and 65 kDa, while the molecular weight of the purified wild-type enzyme was 66 kDa. Random amplified polymorphic DNA and inter-simple sequence repeat markers were used to identify polymorphism and genetic variations between the mutant and wild-type strains.