Screening of high amylase-producing strains by mutagenesis with ultraviolet ray and nitrosoguanidine

Objective To screen high amylase-producing strains by ultraviolet ray(UV) and nitrosoguanidine(NTG).Methods Bacillus cereus SWWL06 as an original strain was induced with UV and NTG respectively,of which the condition was optimized.The strains obtained by mutagenesis with UV-NTG were preliminarily screened according to the ratio of diameter of clear zone to that of colony,and further screened by culture in shake-flask.The obtained high amylase-producting mutants were subcultured continuously and determined for genetic stability.Results The optimal wavelength,time and vertical distance for mutagenesis by UV were 254 nm,120 s and 20 cm respectively.However,the optimal concentration and time for mutagenesis by NTG were 0.5 mg / ml and 40 min respectively.Nine mutants were screened by mutagenesis with UV-NTG.The amylase activity of mutant UV-NTG-3 was 3.515 U / ml,which increased by 3.59 folds as compared with that of original strain SWWL06.However,the amylase activity of mutant UV-NTG-3 after subculture for 10 passages was still 97% of that of the mutant of passage 1.Conclusion A high amylase-producing strain UV-NTG-3 was successfully screened.