Abstract: Pulsed light was applied to mutagenize Bacillus subtilis. The resulting mutants were screened for improved tolerance. The extracellular enzymatic activity and genetic stability of the selected mutants were analyzed and compared with those of the original strain and the differential protein expression of the original strain and the mutant strains was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that 8 resistant mutant strains were generated under the conditions of pulse voltage of 2 450 V, distance of 5 cm and pulse number of 40. After primary and secondary screening, the mutant strains B3 and B7 with good tolerance to high temperature tolerance, acid and high concentration of bile salt were obtained. Their α-amylase activity, protease activity, lipase activity was increased by 67% and 77% (P < 0.01), 56% and 71% (P < 0.01), and 34% and 42% (P < 0.05), compared with those of the original strain, respectively. The enzymatic activity of the obtained mutants was stable (P > 0.05) and showed genetic variation. The protein expression level was different between before and after mutagenesis. These findings proved the feasibility of application of pulsed light to mutagenize B. subtilis.

Key words: tolerance, Bacillus subtilis, pulsed light, mutagenesis and screening, enzymatic activity