Optimization of β-Glucosidase Production by Aspergillus terreus Strain EMOO 6-4 Using Response Surface Methodology Under Solid-State Fermentation

Forty-two morphologically different fungal strains were isolated from different soil samples and agricultural wastes and screened for beta-glucosidase activity under solid-state fermentation. Eight species were chosen as the most active beta-glucosidase producers and were subjected to primary morphological identification. beta-Glucosidase was highly produced by Aspergillus terreus, which showed the highest activity, and was subjected to full identification using scanning electron microscopy and molecular identification. Initial screening of different variables affecting beta-glucosidase production was performed using Plackett-Burman design and the variables with statistically significant effects were identified. The optimal levels of the most significant variables with positive effect and the effect of their mutual interactions on beta-glucosidase production were determined using Box-Behnken design. Fifteen variables including temperature, pH, incubation time, inoculum size, moisture content, substrate concentration, NaNO3, KH2PO4, MgSO4 center dot 7H(2)O, KCl, CaCl2, yeast extract, FeSO4 center dot 7H(2)O, Tween 80, and (NH4)(2)SO4 were screened in 20 experimental runs. Among the 15 variables, NaNO3, KH2PO4 and Tween 80 were found as the most significant factors with positive effect on beta-glucosidase production. The Box-Behnken design was used for further optimization of these selected factors for better beta-glucosidase production. The maximum beta-glucosidase production was 4457.162U g(-1).