Optimization of a heat-tolerant β-glucosidase production by Bacillus sp. ZJ1308 and its purification and characterization

Response surface methodology was used to optimize the medium composition to improve the production of the heat-tolerant β-glucosidase from Bacillus sp. ZJ1308. Three significant factors were found to be corn cob, beef extract, and MnSO4 ·H2 O. The final medium compositions optimized were corn cob (51.8 g/L), beef extract (23.8 g/L), salicin (0.5 g/L), MnSO4 ·H2 O (0.363 g/L), MgSO4 ·7H2 O (0.4 g/L), and NaCl (5 g/L). Under the optimal conditions, the activity of β-glucosidase was up to 4.71 U/mL. β-Glucosidase was purified to homogeneity with a recovery rate of 5% and a specific activity of 110.47 U/mg. The optimal pH and temperature were 7.0 and 60 °C, respectively. β-Glucosidase was stable within a pH range of 6.0-8.0 and showed an extremely high thermostability at 80 and 90 °C, retaining 56% and 38% of its maximal activity, respectively. Ni(2+) and Ba(2+) heavily inhibited the β-glucosidase activity. The purified β-glucosidase showed a high substrate specificity. The kinetic parameters revealed that it had a high catalytic efficiency toward the substrate p-nitrophenyl-β-d-glucopyranoside (Kcat /Km = 700). It also showed a high catalytic activity toward the natural substrate salicin. This study provides a new insight into the future development and use of β-glucosidase from Bacillus sp. ZJ1308.