Rumen protozoa are a hub for diverse hydrogenotrophic functions

Ciliate protozoa are an integral part of the rumen microbial community involved in a variety ofmetabolic processes. These processes are thought to be in part the outcome of interactions withtheir associated prokaryotic community. For example, methane production is facilitated byinterspecies hydrogen transfer between protozoa and archaea. We hypothesize that ciliateprotozoa are host to a stable prokaryotic community dictated by specific functions they carry. Herewe modify the microbial community by varying the forage to concentrate ratios and show that,despite major changes in the prokaryotic community, several taxa remain stably associated withciliate protozoa. By quantifying genes belonging to various known reduction pathways in therumen, we find that the bacterial community associated with protozoa is enriched in genesbelonging to hydrogen utilization pathways and that these genes correspond to the sametaxonomic affiliations seen enriched in protozoa. Our results show that ciliate protozoa in therumen may serve as a hub for various hydrogenotrophic functions and a better understanding ofthe processes driven by different protozoa may unveil potential role of ciliates in shaping rumenmetabolism.