Functional characterization of endoglucanase (CelB) isolated from lignocellulose-degrading microbial consortium for biomass saccharification

Abstract

Culture-independent metagenomic gene discovery allows exploration of genetic resources from uncultured microorganisms. In this study, an endoglucanase gene ( celB ) was identified from metagenomic DNA derived from a structurally stable thermophilic microbial consortium isolated from sugarcane bagasse collection site. CelB endoglucanase was classified in glycosyl hydrolase family 8 with 99% sequence identity to the homolog from Clostridium josui . The recombinant CelB was expressed in Escherichia coli and the purified enzyme exhibited the maximum activity on carboxymethylcellulose (CMC) with a specific activity of 86.17 U/mg at 60 °C, pH 5.0. The recombinant CelB showed specific cleavage pattern by releasing cellobiose (C2) as the major product from cellooligosaccharides (C3 to C6) substrates while C2–C4 were produced from hydrolysis of polysaccharides . The enzyme effectively released reducing sugars with the highest yield from corn stover followed by rice straw and sugarcane bagasse. In addition, supplementation of CelB at 10 mg/g biomass to Accellerase® 1500 (1 mg/g biomass) led to an improved hydrolysis on alkaline-pretreated sugarcane bagasse with 47% increase in glucose yield compared with using Accellerase® 1500 alone. Overall, the enzyme is a potential candidate for cellooligosaccharide production and saccharification of lignocellulosic materials in bio-industries. • CelB was isolated from metagenome of stable cellulolytic consortium. • CelB was classified as a GH8 endoglucanase related to Clostidium josui. • Recombinant CelB expressed in E. coli showed optimal activity at 60 °C, pH 5.0. • C2–C4 were the major product from hydrolysis of cellulosic substrates. • Additive effect of CelB to Accellerase 1500 was demonstrated at low FPU.