Activity and properties of fumarate reductase in ruminal bacteria

Fumarate-reducing bacteria were sought from the main ruminal bacteria, Fibr obacter succinogenes, Selenomonas ruminantium subsp, ruminantium, Selenomon as ruminantium subsp. lactilytica, and Veillonella parvula reduced fumarate by using H-2 as an electron donor. Ruminococcus albus, Prevotella ruminico la, and Anaerovibrio lipolytica consumed fumarate, although they did not ox idize H-2. Of these bacteria, V, parvula, two strains of Selenomonas, and F . succinogenes had a high capacity to reduce fumarate. In all the fumarate- reducing bacteria examined, fumarate reductase existed in the membrane frac tion. Based on the activity per cell mass and the affinity of fumarate redu ctase to fumarate, these bacteria were divided into two groups, which corre sponded to the capacity to use H-2: A group of bacteria with higher activit y and affinity were able to use H-2 as an electron donor for fumarate reduc tion. The bacteria in this group should gain an advantage over the bacteria in another group in fumarate reduction in the rumen. Cellulose digestion b y R. albus was improved by fumarate reduction by S. lactilytica as a result of an increased growth of R. albus, which may have been caused by the fact that S. lactilytica immediately consumed H-2 produced by R. albus. Thus fu marate reduction may play an important role in keeping a low partial pressu re of H-2 in the rumen.