A novel high molecular weight thermo-acidoactive β-glucosidase from Beauveria bassiana

An extracellular high molecular weight β-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 β-glucosidase activity was produced with wheat bran at the concentration of 3%. Glucose caused a repressor effect on the β-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 β-glucosidase with high molecular weight between 400 and 600 kDa. The enzymatic preparation was characterized and showed temperature and pH optima of 55°C and 5.0, respectively. The enzyme was stable at 40 and 50°C but its stability declined at 60°C. Interestingly, this β-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, Ba 2+ was revealed as an activator. This is the first report that focuses on the production and the biochemical characterization of a β-glucosidase from the entomopathogenic fungus, B. bassiana .