Purification and partial characterization of a thermostable alkaline protease from Bacillus licheniformis LHSB-05 isolated from hot spring

An alkaline protease produced from Bacillus licheniformis LHSB-05 isolated from Nigerian hot spring was purified in a 2-step procedure by ammonium sulphate precipitation and Sephacryl S-300 gel filtration chromatography. The enzyme was purified 13.4-fold with a yield of 6.6%. The molecular weight of the protease was 16 kDa on SDS-PAGE. The purified protease had optimum temperature of 50°C. The enzyme retained 90% of its maximum activity at 60°C and had 45% relative activity at 70°C. This enzyme exhibited high thermostability with 100% stability at 50°C and almost 80% stability at 60°C after 60 min of incubation. The protease had optimum pH of 9.0 and showed relative activity between 81 and 71% in the pH range of 10.0 to 12.0. The enzyme was stable over a broad pH range (6.0 to 12.0). Ca2+ and Mg2+ increased protease activity with 27 and 9%, whereas Hg2+ strongly inhibited its activity by 83%. The enzyme was relatively stable in the presence of Ca2+, Mg2+, Al3+, Zn2+ and ethylene diamine tetra acetic acid (EDTA). These characteristics suggest the suitability of protease from B. licheniformis LHSB-05 for use in detergent industries.   Key words: Alkaline protease, Bacillus licheniformis LHSB-05, characterization, purification, thermostability.