Abstract:

An efficient protease–producing and facultative anaerobic bacterium B-1 was isolated from naturally fermented
Douchi by transparent inhibition zone plate assay. The diameter of inhibition zones in anaerobic conditions was found to be
bigger than in aerobic conditions. Based on physiological and biochemical identification and 16S rRNA sequence analysis, it
was identified as Bacillus methylotrophicus. Meanwhile, this study revealed that the optimal pH and temperature for protease
activity and stability from Bacillus methylotrophicus B-1 were pH 7.0 and 40 ℃, respectively. The protease activity was
activated by Mn2+. In addition, Bacillus methylotrophicus B-1 and Bacillus subtilis A-12 were used at an inoculum size of 6%
on raw soybean meal to study the effect of fermentation on the contents of crude protein and small peptides and hydrolysis
degree. The results showed that the content of small peptides and hydrolysis degree of soybean meal fermented by Bacillus
methylotrophicus B-1 were 28.37% and 29.55%, which were 9.04% and 16.07% higher than those of that fermented by
Bacillus subtilis A-12, and 27.22% and 29.13% higher than those of raw soybean meal, respectively.

Key words: protease, facultative anaerobic, Bacillus methylotrophicus, identification, enzymatic properties, fermented soybean meal