Comparative genomic analysis of hemicellulose-degrading potential in bacterial isolates from the anterior intestine of Eisenia andrei (Bouché, 1972)
摘要
Earthworms and their associated microbiota can degrade various types of lignocellulosic residues, but the enzymes, carbohydrate-binding modules, and sugar transporters involved in this process remain imperfectly understood. The present study aimed to identify genes and characterize hemicellulose degradation strategies of bacterial strains with high xylanolytic activity from the earthworm gut. The strains, originally isolated from the anterior intestine of earthworms fed on a diet of palm fiber (Streptomyces thermophilus PF5-2S and Niallia circulans PF7-2S) and coffee husk (Cellulosimicrobium cellulans CH6-3S and Bacillus amyloliquefaciens CH7-2S), were selected for their high xylanolytic activity. We describe shared CAZyme (carbohydrate-active enzyme) genes between the species that encode intracellular accessory enzymes (such as GH51, GH67, and CE7), essential for the depolymerization of branched oligosaccharides, suggesting a cytoplasmic degradation mechanism. We also found that each strain possesses a unique functional repertoire of genes, suggesting a variety of hemicellulolytic strategies that can be attributed to the various isoforms or different carbohydrate-binding modules of these enzymes. Niallia circulans PF7-2S and Bacillus amyloliquefaciens CH7-2S share most of their esterase-encoding CAZyme genes, which allow them to deacetylate hemicellulose. Both Actinobacteria and Firmicutes included in this study form associations in the earthworm gut microenvironment employing different (selfish and communal) and similar mechanisms to accelerate and regulate the degradation of plant biomass. That could explain why the earthworm can efficiently degrade different types of waste. Knowing the molecular aspects involved in the degradation of hemicellulose in the intestinal environment of Eisenia andrei as a study model is essential for bioprospecting purposes in the management and utilization of plant residues.