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About: Methanogenesis is a(n) research topic. Over the lifetime, 5064 publication(s) have been published within this topic receiving 244478 citation(s). The topic is also known as: methane biosynthetic process & methane biosynthesis. more

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Journal ArticleDOI
05 Oct 2000-Nature
Abstract: A large fraction of globally produced methane is converted to CO2 by anaerobic oxidation in marine sediments. Strong geochemical evidence for net methane consumption in anoxic sediments is based on methane profiles, radiotracer experiments and stable carbon isotope data. But the elusive microorganisms mediating this reaction have not yet been isolated, and the pathway of anaerobic oxidation of methane is insufficiently understood. Recent data suggest that certain archaea reverse the process of methanogenesis by interaction with sulphate-reducing bacteria. Here we provide microscopic evidence for a structured consortium of archaea and sulphate-reducing bacteria, which we identified by fluorescence in situ hybridization using specific 16S rRNA-targeted oligonucleotide probes. In this example of a structured archaeal-bacterial symbiosis, the archaea grow in dense aggregates of about 100 cells and are surrounded by sulphate-reducing bacteria. These aggregates were abundant in gas-hydrate-rich sediments with extremely high rates of methane-based sulphate reduction, and apparently mediate anaerobic oxidation of methane. more

2,452 citations

Journal ArticleDOI
Michael J. Whiticar1Institutions (1)
30 Sep 1999-Chemical Geology
Abstract: The diagenetic cycling of carbon within recent unconsolidated sediments and soils generally can be followed more effectively by discerning changes in the dissolved constituents of the interstitial fluids, rather than by monitoring changes in the bulk or solid organic components. The major dissolved carbon species in diagenetic settings are represented by the two carbon redox end-members CH4 and CO2. Bacterial uptake by methanogens of either CO2 or “preformed” reduced carbon substrates such as acetate, methanol or methylated amines can be tracked with the aid of carbon ( 13 C / 12 C ) and hydrogen ( D/H≡ 2 H/ 1 H ) isotopes. The bacterial reduction of CO2 to CH4 is associated with a kinetic isotope effect (KIE) for carbon which discriminates against 13 C . This leads to carbon isotope separation between CO2 and CH4 (eC) exceeding 95 and gives rise to δ 13 C CH 4 values as negative as −110‰ vs. PDB. The carbon KIE associated with fermentation of methylated substrates is lower (eC is ca. 40 to 60, with δ 13 C CH 4 values of −50‰ to −60‰). Hydrogen isotope effects during methanogenesis of methylated substrates can lead to deuterium depletions as large as δ D CH 4 =−531‰ vs. SMOW, whereas, bacterial D/H discrimination for the CO2-reduction pathway is significantly less (δDCH4 ca. −170‰ to −250‰). These field observations have been confirmed by culture experiments with labeled isotopes, although hydrogen isotope exchange and other factors may influence the hydrogen distributions. Bacterial consumption of CH4, both aerobic and anaerobic, is also associated with KIEs for C and H isotopes that enrich the residual CH4 in the heavier isotopes. Carbon fractionation factors related to CH4 oxidation are generally less than eC=10, although values >20 are known. The KIE for hydrogen (eH) during aerobic and anaerobic CH4 oxidation is between 95 and 285. The differences in C and H isotope ratios of CH4, in combination with the isotope ratios of the coexisting H2O and CO2 pairs, differentiate the various bacterial CH4 generation and consumption pathways, and elucidate the cycling of labile sedimentary carbon. more

2,273 citations

Journal ArticleDOI
Bernhard Schink1Institutions (1)
TL;DR: S syntrophically fermenting bacteria synthesize ATP by substrate-level phosphorylation and reinvest part of the ATP-bound energy into reversed electron transport processes, to release the electrons at a redox level accessible by the partner bacteria and to balance their energy budget. more

Abstract: Fatty acids and alcohols are key intermediates in the methanogenic degradation of organic matter, e.g., in anaerobic sewage sludge digestors or freshwater lake sediments. They are produced by classical fermenting bacteria for disposal of electrons derived in simultaneous substrate oxidations. Methanogenic bacteria can degrade primarily only one-carbon compounds. Therefore, acetate, propionate, ethanol, and their higher homologs have to be fermented further to one-carbon compounds. These fermentations are called secondary or syntrophic fermentations. They are endergonic processes under standard conditions and depend on intimate coupling with methanogenesis. The energetic situation of the prokaryotes cooperating in these processes is problematic: the free energy available in the reactions for total conversion of substrate to methane attributes to each partner amounts of energy in the range of the minimum biochemically convertible energy, i.e., 20 to 25 kJ per mol per reaction. This amount corresponds to one-third of an ATP unit and is equivalent to the energy required for a monovalent ion to cross the charged cytoplasmic membrane. Recent studies have revealed that syntrophically fermenting bacteria synthesize ATP by substrate-level phosphorylation and reinvest part of the ATP-bound energy into reversed electron transport processes, to release the electrons at a redox level accessible by the partner bacteria and to balance their energy budget. These findings allow us to understand the energy economy of these bacteria on the basis of concepts derived from the bioenergetics of other microorganisms. more

1,683 citations


Journal ArticleDOI
Abstract: Two primary methanogenic pathways can be distinguished using the carbon and hydrogen stable isotope composition of the methane as a function of the coexisting carbon dioxide and formation water precursors. Although both pathways may occur in both marine and freshwater sediments. CO2 reduction is dominant in the sulphate-free zone of the former, while acetate fermentation is the major pathway in freshwater sediments. Methane in marine sediments can be defined isotopically by δ13C −110 to −600/%., and δD −250 to −1700‰. In contrast, methane from freshwater sediments ranges from δ13C −65 to −500/%. and δD −400 to −2500/%.. Carbon isotope fractionations (αcCO2-CH4) are generally between 1.05 and 1.09 for marine sediments, while lower in freshwater sediments (1.04 to 1.06). The relationship of the methane to the formation water indicates the source of the hydrogen for CO2 reduction to be the water directly with an associated hydrogen fractionation of −180 ± 200/%.. The CH4-H2O hydrogen fractionation is larger for acetate fermentation due to the transfer of the methyl group during methanogenesis which is depleted in deuterium and accounts for 34 of the hydrogen in the methane. A model is presented showing that the fourth hydrogen via acetate fermentation may ultimately come from the formation water but is isotopically fractionated. Combination of the carbon and hydrogen isotope fractionations (αC, αD) from CH4 with CO2 and H2O respectively, can clearly delineate the CO2 reduction and acetate fermentation environments. Defining the character of the methanogenic types with carbon and hydrogen isotopes not only provides information about the environment of formation, it is also most useful in distinguishing biogenic from thermogenic methane gases. more

1,625 citations

Journal ArticleDOI
Abstract: Methane emission by soils results from antagonistic but correlated microbial activities. Methane is produced in the anaerobic zones of submerged soils by methanogens and is oxidised into CO2 by methanotrophs in the aerobic zones of wetland soils and in upland soils. Methanogens and methanotrophs are ubiquitous in soils where they remain viable under unfavourable conditions. Methane transfer from the soil to the atmosphere occurs mostly through the aerenchyma of aquatic plants, but also by diffusion and as bubbles escaping from wetland soils. Methane sources are mainly wetlands. However 60 to more than 90 % of CH4 produced in the anaerobic zones of wetlands is reoxidised in their aerobic zones (rhizosphere and oxidised soil-water interface). Methane consumption occurs in most soils and exhibits a broad range of values. Highest consumption rates or potentials are observed in soils where methanogenesis is or has been effective and where CH4 concentration is or has been much higher than in the atmosphere (ricefields, swamps, landfills, etc.). Aerobic soils consume atmospheric CH4 but their activities are very low and the micro-organisms involved are largely unknown. Methane emissions by cultivated or natural wetlands are expressed in mg CH4·m–2·h–1 with a median lower than 10 mg CH4·m–2·h–1. Methanotrophy in wetlands is most often expressed with the same unit. Methane oxidation by aerobic upland soils is rarely higher than 0.1 mg CH4·m–2·h–1. Forest soils are the most active, followed by grasslands and cultivated soils. Factors that favour CH4 emission from cultivated wetlands are mostly submersion and organic matter addition. Intermittent drainage and utilisation of the sulphate forms of N-fertilisers reduce CH4 emission. Methane oxidation potential of upland soils is reduced by cultivation, especially by ammonium N-fertiliser application. more

1,510 citations

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Topic's top 5 most impactful authors

Ralf Conrad

66 papers, 7.9K citations

Alfons J. M. Stams

45 papers, 3.3K citations

Gatze Lettinga

33 papers, 2.4K citations

Irini Angelidaki

19 papers, 2K citations

Yaobin Zhang

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