Identification of glycosyl hydrolases from a metagenomic library of microflora in sugarcane bagasse collection site and their cooperative action on cellulose degradation

Abstract

Lignocellulose decomposition is a natural process involving the cooperative action of various glycosyl hydrolases (GH) on plant cell wall components. In this study, a metagenomic library was constructed to capture the genetic diversity of microbes inhabiting an industrial bagasse collection site. A variety of putative genes encoding GH families 2, 3, 5, 9, 11, and 16 were identified using activity-based screening, which showed low to moderate homology to various cellulases and hemicellulases. The recombinant GH9 endoglucanase (Cel9) and GH11 endo-xylanase (Xyn11) were thermophilic with optimal activity between 75°C and 80°C and the maximal activity at slightly acidic to neutral pH range. The enzymes exhibited cooperative activity with Trichoderma reesei cellulase on the degradation of lignocellulosic substrates. Mixture design showed positive interactions among the enzyme components. The optimal combination was determined to be 41.4% Celluclast, 18.0% Cel9, and 40.6% Xyn11 with the predicted relative reducing sugar of 658% when compared to Celluclastalone on hydrolysis of alkaline-pretreated bagasse. The work demonstrates the potential of lignocellulolytic enzymes from a novel uncultured microbial resource for enhancing efficiency of biomass-degrading enzyme systems for bio-industries.