Isolation and characterization of a novel thermostable β-glucosidase from Bacillus subtilis SU40.

A new bacterial strain SU40 with ability to produce thermostable β-glucosidase was isolated from soil located at Puducherry (India) and identified as Bacillus subtilis. The conditions like temperature, pH, carbon and nitrogen sources were optimized conditions for the maximum production of β-glucosidase. The enzyme was purified using ammonium sulphate precipitation and BioSep and HPLC chromatography. Purified enzyme was found to be a monomeric protein with an apparent molecular mass of 38.3 kDa. The enzyme was stable over a wide range of pH and temperatures and exhibited maximal activity at 75°C and pH 12.0. The enzyme was found to retain approximately 60% of maximal activity for 1 h at 70°C and hydrolyzed a wide range of aryl-β-D-glucosides and β-linked oligosaccharides with highest activity towards cellobiose and p-nitrophenyl-β-D-glucopyranoside. The Km and Vmax values of the enzyme were 0.21 μM and 9.38 μmoles mg(-1) min(-1), respectively. The enzyme demonstrated stability in the presence of 0.5% surfactants and was completely inhibited after addition of EDTA and Hg2+ ions. Synergistic action of β-glucosidase from B. subtilis SU40 with endoglucanase from Paenibacillus barcinonensis MG7 completely degraded the rice straw.