Cloning and characterization of a new β-Glucosidase from a metagenomic library of Rumen of cattle feeding with Miscanthus sinensis

BACKGROUND: The study on the second generation bio-fuel is a hot area of current research of renewable energy. Among series of key points in this area, the role of β-glucosidase in the degradation of intermediate gluco-oligosaccharides limits the rate of the complete saccharification of lignocellulose. RESULTS: In this study, a new β-glucosidase gene, unglu135B12, which was isolated from a metagenomic library of rumen of cattle feeding with Miscanthus sinensis by the function-based screening, encodes a 779 amino acid polypeptide that contains a catalytic domain belonging to glycoside hydrolase family 3 (GH3). It was recombinantly expressed, purified and biochemically characterized. The recombinant β-glucosidase, unglu135B12, displayed optimum enzymatic activity at pH 5.0 at 38°C, and showed the highest specific activity of 2.5 × 10(3) U/mg under this optimal condition to p-nitrophenyl-β-D-glucopyranoside (pNPG), and its Km and Vmax values were 0.309 mmol/L and 7.292 μmol/min, respectively. In addition, the presence of Ca(2+), K(+), Na(+) slightly improved β-glucosidase activity of unglu135B12 by about 5%, while about 10 ~ 85% loss of β-glucosidase activity was induced by addition of Mn(2+), Fe(3+), Zn(2+), Cu(2+). Interestingly, unglu135B12 was activated by glucose at the concentration lower than 40 mM. CONCLUSIONS: Our findings indicate that unglu135B12 is a new β-glucosidase derived from rumen of cattle, and it might be a potent candidate for saccharification of lignocellulose in industrial application. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/1472-6750-14-85) contains supplementary material, which is available to authorized users.