Does adding a combination of methane inhibitors with different modes of action alter bacterial population structure and function in a long-term simulation of rumen fermentation

Here we explore the effect of a potent direct inhibitor of methanogenesis (chloroform) with or without additives that act as hydrogen sinks (nitrate) or decrease hydrogen production (saponins, through inhibition of protozoa metabolism) on rumen function and the structure of the rumen bacterial population, in a long term rumen simulating fermenter. Both chloroform and nitrate decreased methane production. Chloroform addition was associated with lower levels of volatile fatty acid production and the recovery of 2H in the fermenter, calculated from volatile fatty acid and methane production, was lower in chloroform supplemented vessels in the absence but not the presence of nitrate, suggesting that 2H might have accumulated in chloroform supplemented vessels in the absence but not the presence of nitrate. The bacterial community determined by NGS sequencing was significantly altered by chloroform in control and saponin supplemented vessels but not when nitrate was present suggesting that direct methane inhibition should be combined with the addition of alternative hydrogen sinks in order to promote the adaptive process in the rumen and avoid deleterious effects on rumen fermentation.