Most methanogenic Archaea are hydrogenotrophic, specializing in the use of hydrogen to reduce CO2 to methane. Even though these organisms have multiple hydrogenases that use hydrogen, there is good potential to use them for the net production of hydrogen. This is because some species can use alternative electron donors, most notably formate, and because some species have nitrogenases that can p...

As many of the methanogens first encountered at hydrothermal vents were thermophilic to hyperthermophilic and comprised one of the lower roots of the evolutionary tree, it has been assumed that methanogenesis was one of the earliest, if not the earliest, pathway to life. It being well known that hydrothermal springs associated with serpentinization also bore abiotic methane, it had been further...

The objective of this study was to evaluate the role of reductive acetogenesis as an alternative H2 disposal mechanism in the rumen. H2/CO2-supported acetogenic ruminal bacteria were enumerated by using a selective inhibitor of methanogenesis, 2-bromoethanesulfonic acid (BES). Acetogenic bacteria ranged in density from 2.5 x 10(5) cells/ml in beef cows fed a high-forage diet to 75 cells/ml in f...

A series of laboratory studies were conducted to increase understanding of stable carbon (C/C) and hydrogen (D/H) isotope fractionation arising from methanogenesis by moderately thermophilic acetateand hydrogen-consuming methanogens. Studies of the aceticlastic reaction were conducted with two closely related strains of Methanosaeta thermophila. Results demonstrate a carbon isotope fractionatio...

Microbial methanogenesis at extreme conditions of saline alkaline soda lakes has, so far, been poorly investigated. Despite the obvious domination of sulfidogenesis as the therminal anaerobic process in the hypersaline soda lakes of Kulunda Steppe (Altai, southwestern Siberia), high concentrations of methane were detected in the anaerobic sediments. Potential activity measurements with differen...

Anaerobic digestion is a complex process involving hydrolysis, acidogenesis, acetogenesis and methanogenesis. The separation of the hydrogen-yielding (dark fermentation) and methane-yielding steps under controlled conditions permits the production of hydrogen and methane from biomass. The characterization of microbial communities developed in bioreactors is crucial for the understanding and opt...

The degradation of organic matter by methanogenesis is the most complex and the most efficient way of transforming organic matter into an energetically useful product. It is the dominant process in every anoxic environment where nitrate, sulfate, oxidized iron, or manganese species have been reduced, and where only CO2 is available as a terminal electron acceptor. Moreover, methanogenesis is th...

Methane hydrate found in marine sediments is thought to contain gigaton quantities of methane and is considered an important potential fuel source and climate-forcing agent. Much of the methane in hydrates is biogenic, so models that predict the presence and distribution of hydrates require accurate rates of in situ methanogenesis. We estimated the in situ methanogenesis rates in Hydrate Ridge ...

A study of anaerobic sediments below cyanobacterial mats of a low-salinity meltwater pond called Orange Pond on the McMurdo Ice Shelf at temperatures simulating those in the summer season (<5 degrees C) revealed that both sulfate reduction and methane production were important terminal anaerobic processes. Addition of [2-(14)C]acetate to sediment samples resulted in the passage of label mainly ...