Abstract:

The original strain Bacillus brevis XZE116 producing elastase preserved in our laboratory was treated with
ultraviolet radiation and nitrosoguanidine (NTG) in combination. A high yield elastase-producing strain named as
XZU21 was obtained according to hydrolysis zones and shaking flask fermentation. Its enzyme activity was increased
to 160.3 U/mL, which exhibited 1.67 times higher than that of the original strain XZE116. Its high capacity for
producing elastase remained stable after subculture for ten passages. The optimal pH of the enzyme from the mutant
XZU21 was approximately 9.5 and optimal temperature was 20 ℃, showing 5 ℃ lower than that of the original strain.
The enzyme of the mutant XZU21 was stable blow 60 ℃ and pH 7.0 to 11.5. The enzyme activity could be stimulated
by Mg2+, whereas Pb2+ and Hg2+ almost entirely inhibited the elastase activity. Its activity was strongly inhibited by
serine-protease inhibitors like PSFM, suggesting that the enzyme is a serine protease. These results indicated that the
combined mutation with ultraviolet radiation and nitrosoguanidine had a significant effect for increasing elastase yield
and reducing reaction temperature.

Key words: elastase, combined mutation, mutant, enzymatic characterization