Production and partial purification of protease by selected bacterial strains using raw milk as substrate

Aims: The present study was investigated to optimize and partially purify the proteases produced by the food borne bacterial strains. Methodology and Results: Four bacterial strains such as Bacillus cereus, Proteus vulgaris, P. mirabilis and Enterobacter aerogenes were isolated from food wastes. These strains were individually inoculated in to the formulated culture media supplied with three different concentrations (1:1 to 1:3) of raw milk as major substrate. Among the concentrations, 1:2 ratio of substrate supplied medium showed maximum (0.133 to 8.000 IU/mL) protease production by all the tested organisms. After optimization, the organisms were tested for protease production at various pH (3 to 9), and temperature (30 to 80 °C). The result showed that all the organisms were capable of producing maximum protease at pH 6 (8.533 to 10.133 IU/mL) and at 50 °C (8.666 to 10.666 IU/mL). The crude enzymes produced by the tested organisms were individually purified by two different methods viz sodium alginate and ammonium sulphate-butanol methods. The purity of the protease determined in these two methods was ranged between 3.24 to 5.44 I and 3.13 to 5.55 IU/mL respectively. The partially purified enzymes were further analysed through SDS-PAGE; accordingly the molecular weight of protein produced by the test organisms was determined in between 49.44 and 50.98 kDa. Conclusion, significance and impact of study: Among the tested strains P. vulgaris was identified as the major protease producer in optimized culture condition of 50o C and pH6. The molecular mass of the partially purified protease of P. vulgaris was 50.32 KDa. Further research on optimization of other fermentation parameters using statistical tools with P. vulgaris is needed to scale up the process.