The mutagenesis of Bacillus subtilis was carried out using ultraviolet radiation and ion beams.The purpose was to compare and select stable strains with high nattokinase production,and optimize the fermentation conditions of the mutated strain to further enhance enzyme activity.The research findings in-dicated that strain B subtilis IB-2 was eventually obtained,which exhibited high enzyme activity and strong stability.The enzyme activity of the ion beam-induced mutant strain B subtilis IB-2 reached 320 FU/mL,representing a 19.4%increase compared to the initial strain.The optimal fermentation con-ditions were determined as follows:fermentation time of 33.5 h,inoculum size of 7.5%,seed age of 9 h,temperature of 37℃,and rotation speed of 200 r/min.Under these conditions,the enzyme activity of nat-tokinase reached 355.07 FU/mL,which was basically consistent with the predicted value.The enzyme activity of nattokinase was improved by 10.2%compared to the pre-optimized state.
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