Abstract: In this study, a strain with the capability of producing a high yield of protease, named CL-10, was isolated from the sewage of a canteen in Nanchang University and was identified as Bacillus amyloliquefaciens through physiological and biochemical tests and 16S rRNA sequencing. Rapeseed meal was used as a cheap nitrogen source to produce protease by the strain. The selection and optimization of medium constituents as well as their levels for improved production of protease were carried out using one-factor-at-a-time (OFAT) method combined with response surface methodology (RSM). Rapeseed meal, corn meal and wheat bran levels were selected as independent variables for Box-Behnken design. As a result, the optimal levels for rapeseed meal, corn flour, wheat bran, Tween 20 and ZnSO4·7H2O were determined as 6.1%, 4.4%, 3.2%, 0.7% (V/V), and 0.2%, respectively. Confirmatory experiments performed under these conditions yielded a maximum protease activity of 6 385.1 U/mL, which was increased 2.35-fold compared with the basal fermentation medium, accompanied by a 54.6% reduction in the average cost of nitrogen source. The established process had the advantages of producing high enzymatic activity, low cost, and simple operation. Our results can guide the resource utilization of rapeseed meal for the production of protease.

Key words: strain screening; protease; Bacillus amyloliquefaciens; rapeseed meal; response surface optimization