A Novel High Molecular Weight Thermo-Acidoactive β-Glucosidase from Beauveria bassiana

An extracellular high molecular weight beta-glucosidase was secreted by a local strain P1 of Beauveria bassiana. The enzyme was produced in the presence of various carbon sources, namely glucose, maltose, lactose, glycerol, starch, wheat bran and gruel. The highest level of beta-glucosidase activity was produced with wheat bran at the concentration of 3%. Glucose caused a repressor effect on the beta-glucosidase expression in a dose-dependent manner. The highest enzyme production level was obtained at initial pH of 6.0 and 7.0 in the culture medium. The zymography analysis revealed that B. bassiana secreted a beta-glucosidase with high molecular weight between 400 and 600 kDa. The enzymatic preparation was characterized and showed temperature and pH optima of 55A degrees C and 5.0, respectively. The enzyme was stable at 40 and 50A degrees C but its stability declined at 60A degrees C. Interestingly, this beta-glucosidase had high stability at acid and basic pH saving its initial activity after 24 h incubation at pH from 3.0 to 11.0. It was stable also in presence of monovalent Na+ and K+ ions saving 60% of its initial activity at 2 M salts. Bivalent metal ions preserved totally or partially the enzymatic activity; in addition, Ba2+ was revealed as an activator. This is the first report that focuses on the production and the biochemical characterization of a beta-glucosidase from the entomopathogenic fungus, B. bassiana.