PNNL

Abstract

Ruminants have co-evolved with their gastrointestinal microbial communities that aid in the digestion of plant materials, 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. To identify microorganisms capable of degrading climatedriven increases in woody biomass in arctic and boreal regions, we sampled rumen fluids from Alaskan moose foraging along a seasonal lignocellulose gradient. Winter diets with increased hemicellulose and lignin enriched for BS11, a Bacteroidetes family lacking cultivated or genomically sampled representatives. Our findings show that the BS11 are cosmopolitan host-associated bacteria prevalent in gastrointestinal tracts of ruminants and other mammals, including humans. 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 sugars to short-chain fatty acids, metabolites vital for ruminant energy. Active hemicellulosic fermentation, as well as butyrate and acetate production, were validated by shotgun proteomics and rumen metabolite detection using NMR, illuminating the vital role BS11 play in carbon transformations within the rumen. These results demonstrate that woody biomass selects for BS11 members, providing arctic herbivores with metabolic redundancy to sustain energy generation in a changing vegetative environment.