Influence of CO2 and low concentrations of O2 on fermentative metabolism of the ruminal ciliate Polyplastron multivesiculatum

Abstract

The effects of ruminal concentrations of CO2 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, H2, and CO2. 13C nuclear magnetic resonance spectroscopy identified glycerol as a previously unknown major product of D-[1-13C]glucose fermentation by this protozoan. Metabolite formation rates were clearly influenced by the headspace gas composition. In the presence of 1 to 3 ,uM 02, acetate, H2, and CO2 formation was partially depressed. A gas headspace with a high CO2 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 02 for up to 3 h at 1 kPa of 02. Under gas phases of >2.6 kPa of 02, the organisms rapidly became vacuolate and the cilia became inactive. The results suggest that fermentative pathways in P. multivesiculatum are influenced by the 02 and CO2 concentrations that prevail in situ in the rumen.

Hydrogen Concentration Profiles at the Oxic-Anoxic Interface: a Microsensor Study of the Hindgut of the Wood-Feeding Lower Termite Reticulitermes flavipes (Kollar)

“…In a recent study, we were able to show that O 2 has a strong influence on the metabolic product pattern of the numerically dominant population of lactic acid bacteria in the R. flavipes hindgut (36). This may also be true for termite gut protozoa, since similar shifts in fermentation product patterns in the presence of low O 2 partial pressures were also reported for "anaerobic" rumen ciliates (12). After all, a metabolism according to equation 1 is quite problematic at high H 2 partial pressures.…”

Glycerol: An unexpected major metabolite of energy metabolism by the human malaria parasite

“…However, data from this study suggest that glycerol can be generated by the malaria parasite during asexual growth. The formation of glycerol is unusual amongst eukaryotes (note glycerol is not produced by uninfected human erythrocytes [ 18 ], nor was it detected in control experiments), although it is a feature of anaerobic glucose catabolism in yeast [ 19 ], protozoan parasites such as trichomonas [ 20 ], leishmania [ 21 ] and trypanosomes [ 22 ], as well as rumen ciliates such as Dasytricha [ 23 ], Eudiplodinium [ 24 ], and Polyplastron [ 25 ]. Interestingly, in all of these studies 13 C-NMR spectroscopy was the method adopted for the identification of glycerol.…”

Some rumen ciliates have endosymbiotic methanogens

“…There is no established case of more than one type of endosymbiotic methanogen coexisting in an anaerobic ciliate. Rumen entodiniomorphid and isotrichid holotrich ciliates have been shown to produce about 20 pmol H z h -1 [14,15,20,21,22]. If this is consumed by endosymbiotic methanogens, they will produce 5 pmol CH4/ciliate/h [16].…”