Influence of UV Mutagenesis on ?2-MannanaseProduction Potential of Aspergillus glaucaus andRhizopus japonicus

摘要

Aim: The present study was conducted to improve the β-mannanase production from Aspergillus glaucaus and Rhizopus japonicus using UV mutation.Study Design: The first experiment, spore suspensions of A. glaucaus and R. japonicus was exposed to UV irradiation, while in the second experiment, wild types and mutant strains of A. glaucaus and R. japonicus were screened for β-mannanase production in submerged fermentation.Place and Duration of Study: Microbiology Research Laboratory Federal University of Technology, Akure, Ondo State, Nigeria between July and August, 2012.Methodology: Mutants of A. glaucaus and R. japonicus were generated by exposure of spores suspension to UV irradiation for a period of 110 minutes at a distance of 13 cm in dark from the centre of germicidal lamp (240 nm) at 10 min intervals, 1 ml spores suspension was withdrawn and plated on Malt Extract Agar (MEA). The developed mutants and wild parents were screened for β-mannanase production in submerged fermentation. Quantitatively, β-mannanase activity was determined using dinitrosalicylic acid method, while protein content was determined by Lowry method.Results: Eleven UV mutant fungal strains were generated for each of the wild types (A. glaucaus and R. japonicus) within 110 min of spore exposure to UV irradiation. The amount of enzyme produced by the mutants varied with the time of exposure. Approximately 27% of the mutant of A. glaucaus (9A1UV30, 9A1UV50 and 9A1UV70) generated from 30, 50 and 70 min of exposure to UV irradiation showed higher increase in β-mannanase activities when compared with parent strain, while repression of enzyme biosynthesis was observed in other mutants. Of all the mutants generated, the 9A1UV30 mutant had the highest increase in mannanase activity with approximately 46% higher than the parent strain, while the mutant 9A1UV10 exhibited 0% enzyme activity. Beta-mannanase production potential was repressed in the mutants of R. japonicus except for mutant 9A2UV50 where unappreciable higher increase of enzyme activity of 100.90% was observed in comparison with the parent strain.Conclusion: Enhanced β-mannanase production was obtained from mutant strains 9A1UV30, 9A1UV50 and 9A1UV70 of A. glaucaus and they could be exploited commercially for industrial production of β-mannanase to meet industrial demand. To the best of my knowledge, this is the first report on successful mannanase producer mutants of A. glaucaus and R. japonicus and it is suggested that molecular studies should be carried out on the improved mutants to reveal the mutation.