Characterization of three bacterial glycoside hydrolase family 9 endoglucanases with different modular architectures isolated from a compost metagenome

• Published in: Biochimica et biophysica acta. General subjects Vol. 1865; no. 5; p. 129848
• Main Authors: Aymé, Laure, Hébert, Agnès, Henrissat, Bernard, Lombard, Vincent, Franche, Nathalie, Perret, Stéphanie, Jourdier, Etienne, Heiss-Blanquet, Senta
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2021; Elsevier
• Subjects: active sites; bacteria; bacterial biomass; behavior; cellobiose; cellulose; Cellulose hydrolysis; composts; degradation; digestion; Endoglucanase; Environmental Sciences; genes; Glycoside hydrolase; glycosides; hydrolysis; Life Sciences; lignocellulases; Metagenome; metagenomics; phylogeny; screening; substrate specificity; synergism; Endoglucanase; Metagenome; Cellulose hydrolysis; Glycoside hydrolase; endoglucanase; cellulose hydrolysis; glycoside hydrolase; metagenome
• ISSN: 0304-4165; 1872-8006; 1872-8006
• DOI: 10.1016/j.bbagen.2021.129848

Environmental bacteria express a wide diversity of glycoside hydrolases (GH). Screening and characterization of GH from metagenomic sources provides an insight into biomass degradation strategies of non-cultivated prokaryotes. In the present report, we screened a compost metagenome for lignocellulolytic activities and identified six genes encoding enzymes belonging to family GH9 (GH9a-f). Three of these enzymes (GH9b, GH9d and GH9e) were successfully expressed and characterized. A phylogenetic analysis of the catalytic domain of pro- and eukaryotic GH9 enzymes suggested the existence of two major subgroups. Bacterial GH9s displayed a wide variety of modular architectures and those harboring an N-terminal Ig-like domain, such as GH9b and GH9d, segregated from the remainder. We purified and characterized GH9 endoglucanases from both subgroups and examined their stabilities, substrate specificities and product profiles. GH9e exhibited an original hydrolysis pattern, liberating an elevated proportion of oligosaccharides longer than cellobiose. All of the enzymes exhibited processive behavior and a synergistic action on crystalline cellulose. Synergy was also evidenced between GH9d and a GH48 enzyme identified from the same metagenome. The characterized GH9 enzymes displayed different modular architectures and distinct substrate and product profiles. The presence of a cellulose binding domain was shown to be necessary for binding and digestion of insoluble cellulosic substrates, but not for processivity. The identification of six GH9 enzymes from a compost metagenome and the functional variety of three characterized members highlight the importance of this enzyme family in bacterial biomass deconstruction. •Three metagenomic GH9 cellulases of different modular structures were characterized.•Phylogenetic analysis revealed high structural diversity of bacterial GH9 enzymes.•GH9e harboring a CBM2 and a CBM3 domain shows an original hydrolysis pattern.•GH9d with CBM2 and CBM4 has similar activity on amorphous and crystalline cellulose.•Synergy with a metagenomic GH48 cellulase was evidenced.