Effect of the addition of fumarate on methane production by ruminal microorganisms in vitro

The effect of fumarate used as a feed additive on the reduction of methanog enesis in the rumen was evaluated by in vitro experiments. The addition of fumarate to the culture of mixed ruminal microorganisms that were fermentin g hay powder and concentrate reduced methane production. Most fumarate was metabolized to propionate, and a slight increase was noted in other volatil e fatty acids. Fumarate was utilized by mixed bacteria but not by mixed pro tozoa. Fibrobacter succinogenes, Selenomonas ruminantium ssp. ruminantium, Selenomonas ruminantium ssp. lactilytica, Veillonella parvula, and Wollinel la succinogenes oxidized H-2 by using fumarate as a final electron acceptor , suggesting that these bacteria compete with methanogens for H-2, which is the main substrate for methanogenesis in the rumen. However, the affinity of these bacteria to H-2 was lower than their affinity to methanogens. Thes e fumarate-utilizing bacteria metabolized malate to products that were simi lar to those from fumarate, suggesting the possession of fumarate dehydrata se. Fibrobacter succinogenes, V. parvula, and W. succinogenes utilized form ate, another substrate for methanogenesis, as an electron donor for fumarat e reduction. The affinity of these bacteria to formate was higher than the affinity methanogens have for formate. When methanogens were cocultured wit h an equal cellular amount of each of the fumarate-utilizing bacteria, meth ane production was markedly decreased, not only from formate, but also from H-2. These results suggest that the addition of fumarate to ruminant feed reduces methanogenesis and enhances propionate production in the rumen.