Microbial ecology of hydrogenotrophic rumen microorganisms in response to methane inhibition

Summary

​Management of hydrogen in the rumen is an important factor to be considered when developing strategies to control ruminant methane emissions since hydrogen can impair digestion and fermentation if it accumulates. The aims of this project were to analyse the effect of a methane inhibitor (bromochloromethane) on methane production, metabolic H flux and subsequent responses in SCFA production and rumen microbial community in small ruminants. It was hypothesized that the rumen microbiota would adapt to inhibition of methanogenesis and shift fermentation to reductive processes which would consume more reducing equivalents, but excessive H2 gas would still accumulate and impair fibre digestion. As predicted, the methane-inhibited rumen appeared to adapt to the high H2 levels by shifting fermentation to propionate which was mediated by an increase in the population of hydrogen-consuming Prevotella, Selenomonas and Porphyromonas spp. As the rumen adapted to the high H2 concentration the flow of metabolic hydrogen into SCFA increased by >20% but the majority of 2H (>80%) which is normally consumed in methane formation was expelled by the animal. Therefore consumption of this excess hydrogen into yielding substrates for the animal will require the provision of dietary supplements to drive hydrogen uptake or augmentation of minor hydrogenotrophic pathways such as autotrophic reductive acetogenesis.​