Influence of CO sub 2 and low concentrations of O sub 2 on fermentative metabolism of the ruminal ciliate Polyplastron multivesiculatum

The effects of ruminal concentrations of CO{sub 2} and oxygen on the end products of endogenous metabolism and fermentation of D-glucose by the ruminal entodiniomorphid ciliate Polyplastron multivesiculatum were investigated. The principal metabolic products were butyric, acetic, and lactic acids, H{sub 2}, and CO{sub 2}. {sup 13}C nuclear magnetic resonance spectroscopy identified glycerol as a previously unknown major product of D-(1-{sup 13}C) glucose fermentation by this protozoan. Metabolite formation rates were clearly influenced by the headspace gas composition. In the presence of 1 to 3 {mu}M O{sub 2}, acetate, H{sub 2}, and CO{sub 2} formation was partially depressed. A gas headspace with a high CO{sub 2} content (66 kPa) was found to suppress hydrogenosomal pathways and to favor butyrate accumulation. Cytochromes were not detected ({lt}2 pmol/mg of protein) in P. multivesiculatum; protozoal suspensions, however, consumed O{sub 2} for up to 3 h at 1 kPa of O{sub 2}. Under gas phases of {gt}2.6 kPa of O{sub 2}, the organisms rapidly became vacuolate and the cilia became inactive. The results suggest that fermentative pathways in P. multivesiculatum are influenced by the O{sub 2} and CO{sub 2} concentrations that prevail in situ in the rumen.