Methanosarcina barkeri

About: Methanosarcina barkeri is a research topic. Over the lifetime, 703 publications have been published within this topic receiving 32151 citations.

Carbon isotope effects associated with aceticlastic methanogenesis.

Abstract: The carbon isotope effects associated with synthesis of methane from acetate have been determined for Methanosarcina barkeri 227 and for methanogenic archaea in sediments of Wintergreen Lake, Michigan. At 37 degrees C, the 13C isotope effect for the reaction acetate (methyl carbon) --> methane, as measured in replicate experiments with M. barkeri, was - 21.3% +/- 0.3%. The isotope effect at the carboxyl portion of acetate was essentially equal, indicating participation of both positions in the rate-determining step, as expected for reactions catalyzed by carbon monoxide dehydrogenase. A similar isotope effect, - 19.2% +/- 0.3% was found for this reaction in the natural community (temperature = 20 degrees C). Given these observations, it has been possible to model the flow of carbon to methane within lake sediment communities and to account for carbon isotope compositions of evolving methane. Extension of the model allows interpretation of seasonal fluctuations in 13C contents of methane in other systems.

Effect of redox potential on methanogenesis by Methanosarcina barkeri

Abstract: Concentrations of 0.5% O2 immediately inhibited CH4 production from methanol by Methanosarcina barkeri. Simultaneously, the redox potential of the medium increased to about +100 mV. However, the rates of CH4 production were not significantly affected, when the redox potential of an anoxic medium was adjusted to values between -420 mV and +100 mV by addition of titanium (III) citrate, sodium dithionite, flavin adenine dinucleotide, or sodium ascorbate. When the redox potential was adjusted to values between -80 mV and +550 mV by means of mixtures of ferrocyanide and ferricyanide, CH4 production was not inhibited until a redox potential of about +420 mV was reached. M. barkeri was able to reduce 0.5 mM ferricyanide solution at +430 mV within 0.005%.

Acetate metabolism in Methanosarcina barkeri.

Abstract: Methanosarcina barkeri was grown by acetate fermentation in complex medium (N2 gas phase). The molar growth yield was 1.6–1.9 g cells/mol methane formed. Under these conditions 63–82% of the methane produced byMethanosarcina strains was derived from the methyl carbon of acetate, indicating that some methane was derived from other media components. Growth was not demonstrated in complex media lacking acetate or mineral acetate medium containing acetate but lacking H2/CO2, methanol, or trypticase and yeast extract. Acetate metabolism byM. barkeri strain MS was further exmined in mineral acetate medium containing H2/CO2 and/or methanol, but lacking cysteine. Under these conditions, more methane was derived from the methyl carbon of acetate than from the carboxyl carbon. Methanogenesis from the methyl group increased with increasing acetate concentration. The methyl carbon contributed up to 42% of the methane formed with H2/CO2 and up to 5% with methanol. Methanol stimulated the oxidation of the methyl group of acetate to CO2. The average rates of methane formation from acetate were 1.3 nomol/min ·ml/culture (0.04mg2 cell dry weight) in defined media (gas phase H2/CO2) and complex media (gas phase N2). Acetate contributed up to 60% of cell carbon formed under the growth conditions examined. Similar quantities of cell carbon were derived from the methyl and carboxyl carbons of acetate, suggesting incorporation of this compound as a two-carbon unit. Incorporated acetate was not preferentially localized in lipid material, as 70% of the incorporated acetate was found in the wall and protein cell fractions. Acetate catabolism was stimulated by pregrowing of cultures in media containing acetate, while acetate anabolism was not influenced. The results are discussed in terms of the differences between the mechanisms of acetate catabolism and anabolism.

Sodium dependence of acetate formation by the acetogenic bacterium Acetobacterium woodii.

Abstract: Growth of Acetobacterium woodii on fructose was stimulated by Na+; this stimulation was paralleled by a shift of the acetate-fructose ratio from 2.1 to 2.7. Growth on H2-CO2 or on methanol plus CO2 was strictly dependent on the presence of sodium ions in the medium. Acetate formation from formaldehyde plus H2-CO by resting cells required Na+, but from methanol plus H2-CO did not. This is analogous to H2-CO2 reduction to methane by Methanosarcina barkeri, which involves a sodium pump (V. Muller, C. Winner, and G. Gottschalk, Eur. J. Biochem. 178:519-525, 1988). This suggests that the reduction of methylenetetrahydrofolate to methyltetrahydrofolate is the Na+-requiring reaction. A sodium gradient (Na+ out/Na+ in = 32, delta pNa = -91 mV) was built up when resting cells of A. woodii were incubated under H2-CO2. Acetogenesis was inhibited when the delta pNa was dissipated by monensin.

Nitrogen fixation by a methanogenic archaebacterium

Abstract: The ability to fix nitrogen (N2) is found among a wide variety of the prokaryotic eubacteria, but not in eukaryotes1. In addition to the prokaryotic eubacteria and eukaryotes, a third ‘kingdom’—the archchaebacteria—has been defined based on the comparison of 16S ribosomal oligonucleotide sequence catalogues2,3. Included in the archaebacterial kingdom are certain obligate halophiles and thermoacidophiles, and the methanogens, strictly anaerobic, methane-producing bacteria4. Here we report diazotrophy by an archaebacterium, the methanogen Methanosarcina barkeri strain 227. Because it has been proposed that the archaebacteria, eubacteria and eukaryotes diverged at an early stage in evolution2,3, the discovery of diazotrophy (N2 fixation) in a member of the archaebacterial group raises interesting evolutionary questions.1