Research on breeding of Bacillus subtilis natto by ultraviolet mutation

To improve the production of Bacillus subtilis natto kinase and select the strain with high thrombolytic ability, the ultraviolet mutation breeding of Bacillus subtilis natto was studied. Four kinds of bacterial suspensions with different nitrogen sources were diluted in proportion and then put into the culture medium to select the best nitrogen source according to the concentration by observing the number of colonies. Milk-agar plate screening method and agar powder-fibrin plate method were used to select the mutagenic strains and enzyme activity. Based on ultraviolet physical mutagenesis, the strains with high enzyme activity yield were selected, and the effects of case fatality rate and positive mutation rate on them were analyzed. The results indicated that the highest positive mutation rate of 3% could be obtained by using 40 W ultraviolet lamp at a distance of 20 cm for 60 s. The highest kinase activity of the obtained high-yield strain was 534.95 U/mL, which was 11.84% higher than that of the original strain.