Ruminants have co-evolved with gastrointestinal microbial communities that aid in the digestion of plant material, providing energy for the host. The ability of this microbiome to adapt to altered host diets may dramatically impact the survival of wild ruminant populations, especially under future climate change scenarios. A recent census of microbial membership from ruminants across the globe revealed several core bacteria conserved across nearly all ruminants, many of which were uncultivated Bacteroidetes. Although these microorganisms are inferred to play key roles in carbon transformations in the rumen, these ubiquitous lineages remain elusive due to a lack of genomic sampling and physiological characterization. To identify potential core microorganisms capable of degrading climate-driven increases in woody biomass in arctic and boreal regions, we sampled rumen fluids from Alaskan moose foraging along a seasonal carbon gradient.
Results/Conclusions
Winter diets with increased hemicellulose and lignin enriched for BS11, a core Bacteroidetes family prevalent across ruminants, but lacking cultivated or genomically sampled representatives. Metagenomic reconstruction yielded the first five BS11 genomes, phylogenetically resolving two genera within this taxonomically undefined family. Genome-enabled metabolic analyses uncovered multiple pathways for degrading hemicellulose to short-chain fatty acids, metabolites vital for ruminant energy. Active BS11 hemicellulosic fermentation as well as butyrate and acetate production were validated by metaproteomics and 1H NMR rumen metabolites, illuminating the vital role BS11 play in carbon transformations within the rumen. These results demonstrate that increased dietary woody biomass selects for BS11, providing arctic herbivores with metabolic redundancy to sustain energy generation in a changing environment.