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Here, we characterize two novel GH5 endoglucanases (GH5CelA and GH5CelB) from an uncultured bacterium identified in termite gut microbiomes. Both genes were codon-optimized, synthetized, cloned, and expressed as recombinant proteins in Escherichia coli for subsequent purification. Both enzymes showed activity on the pNPC and barley β-glucan substrates, whereas GH5CelB also showed low activity on carboxymethyl cellulose. The optimum conditions for both enzymes were an acid pH (5) and moderate temperature (35 to 50 °C). The enzymes differed in the kinetic profiles and patterns of the generated hydrolysis products. A structural-based modeling analysis indicated that both enzymes possess a typical (β/α)8-barrel fold characteristic of GH5 family, with some differential features in the active site cleft. Also, GH5CelB presents a putative secondary binding site. Furthermore, adjacent to the active site of GH5CelA and GH5CelB, a whole subdomain rarely found in GH5 family may participate in substrate binding and thermal stability. Therefore, GH5CelA may be a good candidate for the production of cello-oligosaccharides of different degrees of polymerization applicable for feed and food industries, including prebiotics. On the other hand, GH5CelB could be useful in an enzymatic cocktail for the production of lignocellulosic bioethanol, because of the production of glucose as a hydrolysis product. Key Points • Synthetic metagenomics is a powerful approach for discovering novel enzymes. • Two novel GH5 endoglucanases from nonculturable microorganisms were characterized. • Structural differences between them and other GH5 endoglucanases were observed. • The enzymes may be good candidates for feed, food, and/or bioethanol industries. [ABSTRACT FROM AUTHOR]

In this study, we used shotgun metagenomic sequencing to characterise the microbial metabolic potential for lignocellulose transformation in the gut of two colonies of Argentine higher termite species with different feeding habits, Cortaritermes fulviceps and Nasutitermes aquilinus. Our goal was to assess the microbial community compositions and metabolic capacity, and to identify genes involved in lignocellulose degradation. Individuals from both termite species contained the same five dominant bacterial phyla (Spirochaetes, Firmicutes, Proteobacteria, Fibrobacteres and Bacteroidetes) although with different relative abundances. However, detected functional capacity varied, with C. fulviceps (a grass-wood-feeder) gut microbiome samples containing more genes related to amino acid metabolism, whereas N. aquilinus (a wood-feeder) gut microbiome samples were enriched in genes involved in carbohydrate metabolism and cellulose degradation. The C. fulviceps gut microbiome was enriched specifically in genes coding for debranching- and oligosaccharide-degrading enzymes. These findings suggest an association between the primary food source and the predicted categories of the enzymes present in the gut microbiomes of each species. To further investigate the termite microbiomes as sources of biotechnologically relevant glycosyl hydrolases, a putative GH10 endo-β-1,4-xylanase, Xyl10E, was cloned and expressed in Escherichia coli. Functional analysis of the recombinant metagenome-derived enzyme showed high specificity towards beechwood xylan (288.1 IU/mg), with the optimum activity at 50 °C and a pH-activity range from 5 to 10. These characteristics suggest that Xy110E may be a promising candidate for further development in lignocellulose deconstruction applications. [ABSTRACT FROM AUTHOR]