A metagenomic approach to discover a novel β-glucosidase from bovine rumens

Abstract

β-Glucosidases play an important role in biomass degradation as they hydrolyze cellobiose to glucose in a final step of cellulolysis. In particular, ruminant animals rely on β-glucosidases from rumen microorganisms for conversion of plant cellulosic materials into glucose. In this study, we are interested in characterization of a novel β-glucosidase from rumen microorganisms. However, most rumen microorganisms are obligate anaerobes, which require special cultivation conditions. Presently, the metagenomic techniques, which enable isolation and characterization of microbial genes directly from environmental samples, have been applied to overcome these problems. In this study, the sequence-based screening approach was successfully applied to identify a novel β-glucosidase gene, Br2, from a bovine rumen metagenomic sample. A 1338-bp complete coding sequence of Br2 encodes a 51-kDa GH1 β-glucosidase of 445 amino acid residues with 59% sequence identity to a β-glucosidase from Cellulosilyticum ruminicola JCM 14822. The recombinantly expressed Br2 exhibited an optimal activity at pH 6.5 and 40°C, reflecting its rumen bacterial origin, and relatively higher catalytic efficiencies toward glucoside and fucoside substrates than other glycosides, similar to many previously reported bacterial β-glucosidases. Our sequence-based screening approach can be applied to identify other genes of interest from environmental samples.