Engineering of a Bacillus amyloliquefaciens Strain with High Neutral Protease Producing Capacity and Optimization of Its Fermentation Conditions

The neutral protease has high potential for industrial applications, and attempts to improve enzyme expression level have important application values. In the present study, a neutral protease-encoding gene, Banpr, was cloned from Bacillus amyloliquefaciens strain K11, and a genetic manipulation method specific for this difficult-to-transform strain was developed for the high-level expression of neutral protease. The recombinant plasmid pUB110-Banpr was constructed in Bacillus subtilis strain WB600 and then transformed into strain K11 under optimized conditions. A positive transformant 110N-6 with the highest protease secreting capacity on skim milk plates and great genetic stability for more than 100 generations was selected for further study. Optimization of the fermentation conditions increased the enzyme activity of strain 110N-6 to 8995 ± 250 U/ml in flask culture and 28084 ± 1282 U/ml in 15-l fermentor, which are significantly higher than that of the native strain K11 and industrial strain B. subtilis AS.1398, respectively. The high expression level and extreme genetic stability make B. amyloliquefaciens strain 110N-6 more favorable for mass production of neutral protease for industrial uses.