Abstract: In this study, Bacillus subtilis QLB6 that had been isolated from aged tobacco leaves and been found to have higher proteolytic activity was mutagenized by means of He-Ne laser irradiation. The optimum irradiation dose was determined based on survival rate and positive mutation rate. Based on transparent circle and proteolytic acivity, a target strain was obtained and named QLB6F. The strain exhibited an increase of 219%, 38% and 71% respectively in cellulose, protease and amylase activities when compared to QLB6. After the 30th passage, the genetic stability of the mutant strain remained excellent and no reverse mutation was observed.

Key words: Bacillus subtilis, complex enzymes, He-Ne laser, genetic stability