Identification of a metagenome-derived β-glucosidase from bioreactor contents

A novel β-glucosidase gene designated as bgl1T was cloned by function-based screening of a metagenomic library from uncultured microorganisms in contents of a bioreactor. The gene has an open reading frame of 1860 base pairs and encodes a 620 amino acid polypeptide with a predicted molecular mass of about 65 kDa. The deduced amino acid sequence comparison and phylogenetic analysis indicated that Bgl1T and other putative β-glucoside-specific II ABC subunit components, were closely related. Functional characterization with a high performance liquid chromatography method demonstrated that the recombinant Bgl1T protein hydrolyzed d-(+)-cellobiose to glucose. The maximum activity for Bgl1T protein occurred at pH 7.0 and 37 °C using p-nitrophenyl-β-d-glucoside as the substrate. The putative β-glucosidase had an apparent Km value of 1.45 mM, a Vmax value of 20.5 U/mg, a kcat value of 1370/min and a kcat/Km value of 943/mM/min. The biochemical characterization of Bgl1T protein indicated its potential applications for better industrial production of glucose or ethanol by biological processes under moderate conditions.