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). super(13)C nuclear magnetic resonance spectroscopy identified glycerol as a previously unknown major product of D-(1- super(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 (< 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 >2.6 kPa of O sub(2), the organisms rapidly became vacuolate and the cilia became inactive.