Cloning and expression of β-glucosidase gene from Bacillus licheniformis into E. coli BL 21 (DE3)

A 1.4 Kb fragment of Bacillus licheniformis ATCC 14580 encoding beta-glucosidase was cloned and expressed in Escherichia coli. beta-Glucosidase expressed by E. coli harboring cloned gene was located entirely in the intracellular fraction. Recombinant beta-glucosidase protein was purified to homogeneity level and the molecular weight was found to be 53 kDa using sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. It gave maximum activity at 50 degrees C and pH 6. K-m and V-max were 0.206 mM and 1.26 U/mg, respectively, with p-nitrophenyl-beta-D-glucopyranoside, while activation energy E-a, enthalpy of activation Delta H and entropy of activation Delta S were found to be 66.31 kJ/mol, 64.04 kJ/mol and 48.28 J/mol/K, respectively. The pK(a1) and pK(a2) of the ionizable groups of active site residues involved in V-max were found to be 5.5 and 7.0, respectively. When the recombinant beta-glucosidase protein was used as a member of consortium with endoglucanase and exoglucanase for the saccharification of wheat straw, 123% increase in saccharification was observed.