Purification and partial characterization of serine alkaline metalloprotease from Bacillus brevis MWB-01

Background Proteases from bacteria are among the most important hydrolytic enzymes that have been studied due to their extracellular nature and high yield of production. Of these, alkaline proteases have potential for application in detergent, leather, food, and pharmaceutical industries. However, their usefulness in industry is limited by low activity and stability at high temperatures, extreme pH, presence of organic solvents and detergent ingredients. It is therefore very crucial to search for new alkaline proteases with novel properties from a variety of microbial sources. Results In the present study, 21 Bacillus species isolated from organic waste sites were screened for proteolytic activity on casein agar. Bacillus brevis MWB-01 exhibited highest proteolytic activity with a clear zone diameter of 35 mm. Production of protease from B. brevis MWB-01 was investigated in optimized media after 48 h of cultivation with shaking (180 rpm) at 37°C. The protease was partially purified in a two-step procedure using ammonium sulphate precipitation and gel filtration chromatography on Sephadex G-200 column. The enzyme was purified 2.1-fold with yield of 4.6%. The purified protease had optimum temperature of 40°C with relative activity of about 50% at 50°C and was uniquely stable up to 60°C after 30 min of incubation exhibiting 63% residual activity. The enzyme had optimum pH of 8.0 and remarkably showed relative activity above 70% at pH 9.0 to 11.0 and 53% at pH 12.0, respectively and was very stable over a wide pH range (6.0 to 12.0). Ca 2+ and Mn 2+ increased protease activity with 9.8% and 3.5%, respectively; Hg 2+ and Zn 2+ strongly inhibited protease activity by 89% and 86%. The almost complete inhibition of the enzyme by phenylmethylsulphonyl fluoride (PMSF) and ethylene diamine tetra acetic acid (EDTA) confirmed the enzyme as a serine metalloprotease. The enzyme had highest compatibility with Sunlight, a commercial laundry detergent. Conclusion The characteristics of purified protease from B. brevis MWB-01 reveal the enzyme as a thermotolerant serine alkaline metalloprotease compatible with detergent formulation aids. Results suggest that protease from B. brevis MWB-01 is a good bioresource for industrial applications.