Submitted to: Federation of European Microbiological Societies Microbiology Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/30/2005
Publication Date: 2/15/2006
Citation: Russell, J.B. 2006. Factors affecting lysine degradation by ruminal fusobacteria. Federation of European Microbiological Societies Microbiology Ecology. 56:18-24. Interpretive Summary: Ruminal lysine degradation is a wasteful process that deprives the animal of an essential amino acid, but it is not clear which bacteria were responsible for this degradation. Fusobacterium necrophorum can readily be enriched from the rumen with lysine, and its deamination rate is very rapid. However, when cattle were switched from hay to a ration containing hay, lysine and commercial protein supplement, the lysine deamination rate of the mixed ruminal bacteria did not increase. In vitro experiments indicated that the key factor to prevent the enrichment of lysine-degrading ruminal fusobacteria in vitro and in vivo was the inability of this species to tolerate fermentation acids at acidic pH. Research on ruminal amino acid deamination has the potential to decrease the cost of cattle production.
Technical Abstract: Fusobacterium necrophorum can readily be enriched from the rumen with lysine, and its deamination rate is very rapid rate. However, when cattle were switched from hay to a ration containing hay, lysine and commercial protein supplement, the lysine deamination rate of the mixed ruminal bacteria did not increase. The addition of F. necrophorum JB2 to mixed ruminal bacteria significantly increased lysine degradation, but only if the ratio of ruminal fluid to basal medium was less than 25%. If more ruminal fluid (pH 6.1) was added, growth decreased by as much as 80%. Clarified, autoclaved ruminal was also inhibitory. When F. necrophorum JB2 was grown in a lysine-limited continuous culture (0.1 h-1 dilution rate), and pH was decreased from 6.75 with HCl, optical density decreased linearly. The culture washed-out at pH 5.6. Batch cultures grew as well in basal medium at pH 6.1 as 6.6. Sodium acetate addition (100 mM) only caused a 10% decrease in optical density than pH 6.6, but virtually no growth could be detected if the pH 6.1 and sodium acetate was 100 mM. The negative effect of fermentation acid at low pH was not lysine-specific. Similar decreases in growth were observed if lactate was the energy source. Based on these results, F. necrophorum should not be classified as an acid-resistant ruminal bacterium.