Partial Purification and Characterization of Alkaline Protease from Bacillus brevis Isolated from Milk Processing Waste Site

Abstract

Fifteen alkalophilic Bacillus species isolated from six different waste sites were evaluatedin respect to proteolytic activity on casein agar. Bacillus brevis isolated from milk processing waste site exhibited the highest proteolytic activity with an average diameter of clearance zone measuring 3.5cm. Production of protease from Bacillus brevis was investigated in an optimum medium after 48 hours of cultivation with shaking (180 rpm) at 37oC. The alkaline protease produced was partially purified in a two-step procedure using ammonium sulphate precipitation and gel filtration chromatography on Sephadex G-200. The enzyme was purified 2.1-fold with a yield of 4.6%. The protease had optimum temperature of 40oC. The purified protease was stable up to 60oC after 30 minutes of incubation exhibiting 60% residual activity at that temperature. The enzyme had optimum pH of 8.0 and showed relative activity of 76.1% at pH 9 and 66.1% at pH 10.0 respectively. The purified protease was stable over a wide pH range (6.0-10.0). Ca2+ and Mn2+ increased protease activity with 9.8 and 3.5% respectively. Hg2+ and Zn2+ strongly inhibited protease activity, decreasing the activity by 89.9% and 85.9% respectively. The purified protease had highest compatibility with Sunlight, a commercial detergent. The exhibited characteristics suggest the suitability of protease from Bacillus brevis for industrial application.