Ability of Selenomonas ruminantium, Veillonella parvula, and Wolinella succinogenes to reduce nitrate and nitrite with special reference to the suppression of ruminal methanogenesis

When mixed ruminal microbes were grown in a medium containing ground hay and concentrate, cell numbers of nitrate-reducing bacteria, Veillonella parvula and Wolinella succinogenes, drastically decreased as estimated by competitive PCR. However, decrease in their numbers was prevented by the addition of nitrate, suggesting that energy acquisition by electron transport phosphorylation (ETP) coupled with nitrate and/or nitrite reduction is important for the survival of these bacteria in the rumen. On the other hand, the number of Selenomonas ruminantium increased, and addition of nitrate did not affect the number, suggesting that the numbers of nitrate-reducing strains of S. ruminantium are low. A nitrate-reducing strain of S. ruminantium subsp. lactilytica was found to have the ETP system coupled with both nitrate and nitrite reduction. V. parvula, W. succinogenes, S. ruminantium, and Streptococcus bovis were more tolerant to nitrite toxicity than other representative ruminal bacteria. Methanogens were particularly sensitive to nitrite. W. succinogenes reduced nitrate and nitrite at higher rates than V. parvula and the subsp. lactilytica, but growth of W. succinogenes on nitrate and H-2 was slower than the growth of V. parvula and the subsp. lactilytica. Methane production by unidentified methanogen mixture was markedly reduced by the coexistence of W. succinogenes, V. parvula or the subsp. lactilytica in the presence of nitrate and H-2. W. succinogenes was shown to be most effective to augment nitrate and nitrite reduction, and to reduce methanogenesis. (C) 2003 Elsevier Science Ltd. All rights reserved.