Growth Media Optimization for Production of Alkaline Protease from Industrial Wastewater using Bacillus subtilis PTCC 1254

Abstract

Alkaline proteases are widely used in industrial processes due to their high pH tolerance and thermal stability. In present work, the protease producing ability of Bacillus strains (Bacillus subtilis PTCC 1254, B. subtilis PTCC 1156 and B. subtilis PTCC 1715) was studied. B. subtilis PTCC 1254 showed the highest proteolytic activity and therefore, the strain was selected as the biological agent in the submerged fermentation. Cell growth kinetic model was investigated using Malthus and Logistic equations, which were relatively well fitted to the experimental data. The maximum specific growth rate for Malthus and Logistic models were 0.187 and 0.377 h-1, respectively. The optimum culture conditions were defined as follows: pH 9, temperature 37°C, fermentation time 72 h, agitation speed 150 rpm and 4% inoculum with medium contained 1 g/l CaCl2, 0.6 g/l K2HPO4, 1 g/l KH2PO4, 0.2 g/l MgSO4.7H2O, 2 g/l sugarcane bagasse and 4 g/l corn bran as carbon and nitrogen sources. A 25% v/v industrial wastewater containing starchy waste was used as main substrate. Under optimum conditions, maximum alkaline protease activity of 117.43 U/ml was achieved. Also, the obtained protease was able to remove blood stain from cotton fabric and hydrolyze gelatin of X-ray film. Thus, this protease showed potential applications in detergent and photographic industries.