Expression of Recombinant β-Glucosidase in Bacillus subtilis and Its Enzymatic Characterization and Application in Preparation of Icariside II

To obtain a safe and efficient β-glucosidase for preparing icariside II from icariin by biocatalytic hydrolysis, a GRAS (generally recognized as safe) strain Bacillus subtilis WB600 was used as the host to produce a thermophilic β-glucosidase from Thermotoga petrophila, by construction of a Escherichia coli-Bacillus subtilis shuttle vector pMA5. Enzymatic properties of the recombinant enzyme and its process conditions of hydrolyzing icariin to prepare icariside II were studied. The result showed that after cultivated in SR culture for 48 h at 30 ℃, the activity of β-glucosidase in the fermented broth reached to 69.68 U/mL. TpBgl3 exhibited the maximal activity at 85 °C and pH4.0. More than 85% of the maximum activity was retained after incubation at 65 °C and pH4.0 for 3 h. Under optimized conditions of 65 °C, pH4.0, and 0.16 U/mg enzyme dosage, the recombinant enzyme could transform 10 g/L icariin into 7.50 g/L icariside II in 20 min with a molar conversion of 98.67%. The successful secretory expression of β-glucosidase in Bacillus subtilis could provide new ways to the industrial safe and efficient biopreparation of icariside II and other high-value-added aglycon compounds.