Functional metagenomics reveals considerable lignocellulase gene clusters in the termite gut microbiome

Termites are renowned for an expertise in thriving on wood, which is now known to be largely attributed to their intestinal microbial symbionts. Thus, metagenomes derived from termite guts are natural reservoirs for mining lignocellulase genes. Here, a fosmid library was constructed from the whole gut metagenome of a higher wood-feeding Globitermes brachycerastes Globitermes termites. After functional screening of about 50,000 clones for four major lignocellulases genes, a total of 464 positive clones were obtained, including 267 endoglucanase-positive clones, 24 exoglucanase-positive clones, 72 ß-glucosidase-positive clones and 101 endoxylanase-positive clones. Pyrosequencing of about 170 fosmids clones unveiled considerable bacterial genomic fragments with lignocellulase gene clusters. Among these, four putative GH10 xylanase-encoding genes, three of which share one operon, were further cloned and characterized.