Identification of a Marine Bacterium S-3685 with High Neutral Protease and Optimization of Its Fermentation Conditions

Abstract:

The S-3685 strain, a marine bacterium producing neutral protease, was screened from South China Sea. It was identified as a Bacillus sp. based on the morphology, the biochemical characteristics, and the 16S rDNA sequencing results. This strain was gram-positive, and the spore located in the middle had ellipse or columnar shapes. The bacterial colony was round, protuberance, and milk white on the agar culture-medium. The surface of the bacterial colony was smooth and moist (30℃, 24 h). Over time the colony slightly shriveled bumps in the middle. The length was 2.4−3.2 microns. The strain grew under the pH 5.0−11.0, and could grow normally at the temperature 4−40℃. We then explored the fermentation conditions using a 250 ml shake flask. The optimum sources of carbon and nitrogen were glucose (10 g/L) and pulse flour (10 g/L) respectively, plus the beef extract (5 g/L) and the yeast extract (5 g/L). The optimum concentrations of MgSO4·7H2O, Na2CO3 and KH2PO4 were 0.2 g/L, 2.0 g/L and 1.0 g/L respectively. The optimum initial pH of the culture medium for the protease production was 7.0. The optimized culture conditions were: inoculums at 4%, broth content at 15 ml/250ml(v/v), temperature at 30℃, and culture for 72 h. After the optimization, the productivity of protease was increased by 5 times (from 850 to 4250 U/ml).