Shotgun metagenomics of moose rumen

The moose (Alces alces) manages to utilize energy from fiber-rich lignocellulose material through enzymes produced by the microbes in its rumen. Some of these specialized enzymes may outperform cellulases and hemicellulases that are used in bio-refinery processes today. Shotgun metagenomics offers a method to study microbial communities in detail and to capture the gene sequences coding for enzymes that can be produced in the laboratory. We applied the technique on rumen material from moose. Through a binning approach, a large number of metagenome-assembled genomes (MAGs) from single species and strains were isolated and characterized based on taxonomy and carbohydrate active enzyme (CAZY) profile. Most of the 99 MAGs were classified to the bacterial phyla Bacteriodetes and Firmicutes, which is in agreement with previous studies of rumen from moose and other herbivores. Phylogenomic analysis of MAGs revealed novel clades within Bacteriodetes with no related previously characterized genome. In addition, new genomes that were closely related to the recently described Melainabacteria, newly proposed candidate divisions SR1 and TM7 and previously uncharacterized Alphaproteobacteria were also retrieved. Putative cellulolytic functions were observed in several clades of Bacteroidetes and for MAGs of genus Ruminococcus, Fibrobacteres, and Treponema. Cellulosome components were present in MAGs of Ruminococcus but also in certain clades of Bacteroidetes. Cellulosomes are generally described in the Firmicutes family Clostridiales. Multiple putative cellulases were identified within species from several phyla. At a general level, the most frequently occurring polysaccharide-degrading enzymes targeted hemicellulose, starch and pectin. This study describes the first shotgun-metagenomic characterization of moose rumen and the high number of reconstructed genomes provides a valuable link between phylogeny and cellulolytic role.