Formate Metabolism by Ruminal Microorganisms in Relation to Methanogenesis

Abstract

From the viewpoint that it is desirable to reduce methane production in the rumen by increasing formate utilization by microorganisms other than methanogens, formate metabolism by ruminal microorganisms was examined. Culture experiments with mixed microorganisms indicated that little formate was accumulated even when formate production was rapid, suggesting that the capacity to consume formate usually exceeds the rate of formate production. When methanogenesis was suppressed with anthraquinone (ATQ), formate was accumulated. In a culture with formate added, the amount of formate consumed was stoichiometrically equivalent to the amount of methane produced. These results indicate that almost all formate was utilized by methanogens. Methanogens were found to possess formate dehydrogenase (FDH) and utilize formate after conversion to H2 and CO2. Also mixed microorganisms other than methanogens converted formate to H2, but utilization as a C1 unit was extremely small. Fibrobacter succinogenes, Selenomonas ruminantium, Selenomonas lactilytica, Veillonella parvula, and Anaerovibrio lipolytica consumed formate, indicating the possession of FDH. A mixed culture in which methanogens were suppressed with ATQ produced a higher percentage of propionate, although fermentation was suppressed by accumulated H2. A similar result was obtained when formate was added to a mixed culture in which methanogenesis was eliminated. These results suggest that electrons from H2 can be utilized for propionate-producing reactions, implying that bacteria which carry out such reactions may compete with methanogens for formate, ultimately H2.