New perspectives on anaerobic methane oxidation (original) (raw)
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New perspectives on anaerobic methane oxidation : Minireview
2000
Anaerobic methane oxidation is a globally important but poorly understood process. Four lines of evidence have recently improved our understanding of this process. First, studies of recent marine sediments indicate that a consortium of methanogens and sulphate-reducing bacteria are responsible for anaerobic methane oxidation; a mechanism of`reverse methanogenesis' was proposed, based on the principle of interspecies hydrogen transfer. Second, studies of known methanogens under low hydrogen and high methane conditions were unable to induce methane oxidation, indicating that`reverse methanogenesis' is not a widespread process in methanogens. Third, lipid biomarker studies detected isotopically depleted archaeal and bacterial biomarkers from marine methane vents, and indicate that Archaea are the primary consumers of methane. Finally, phylogenetic studies indicate that only specific groups of Archaea and SRB are involved in methane oxidation. This review integrates results from these recent studies to constrain the responsible mechanisms.
Anaerobic Oxidation of Methane: Progress with an Unknown Process
Annual Review of Microbiology, 2009
Methane is the most abundant hydrocarbon in the atmosphere, and it is an important greenhouse gas, which has so far contributed an estimated 20% of postindustrial global warming. A great deal of biogeochemical research has focused on the causes and effects of the variation in global fluxes of methane throughout earth's history, but the underlying microbial processes and their key agents remain poorly understood. This is a disturbing knowledge gap because 85% of the annual global methane production and about 60% of its consumption are based on microbial processes. Only three key functional groups of microorganisms of limited diversity regulate the fluxes of methane on earth, namely the aerobic methanotrophic bacteria, the methanogenic archaea, and their close relatives, the anaerobic methanotrophic archaea (ANME). The ANME represent special lines of descent within the Euryarchaeota and appear to gain energy exclusively from the anaerobic oxidation of methane (AOM), with sulfate a...
Environmental Microbiology, 2011
Uncultured ANaerobic MEthanotrophic (ANME) archaea are often assumed to be obligate methanotrophs that are incapable of net methanogenesis, and are therefore used as proxies for anaerobic methane oxidation in many environments in spite of uncertainty regarding their metabolic capabilities. Anaerobic methane oxidation regulates methane emissions in marine sediments and appears to occur through a reversal of a methane-producing metabolism. We tested the assumption that ANME are obligate methanotrophs by detecting and quantifying gene transcription of ANME-1 across zones of methane oxidation versus methane production in sediments from the White Oak River estuary, North Carolina. ANME-1 consistently transcribe 16S rRNA and mRNA of methyl coenzyme M reductase (mcrA), the key gene for methanogenesis, up to 45 cm into methanogenic sediments. CARD-FISH shows that ANME-1 exist as single rod-shaped cells or pairs of cells. Integrating normalized depth distributions of 16S rDNA and rRNA (measured with qPCR and RT-qPCR respectively) shows that 26-77% of the rDNA (a proxy for ANME-1 cell numbers), and 18-76% of the rRNA (a proxy for ANME-1 activity) occurs within methane-producing sediments. These results, along with a re-assessment of the published Iiterature, change the perspective to ANME-1 as methanogens that are also capable of methane oxidation.
A genomic view of methane oxidation by aerobic bacteria and anaerobic archaea
Genome biology, 2005
Recent sequencing of the genome and proteomic analysis of a model aerobic methanotrophic bacterium, Methylococcus capsulatus (Bath) has revealed a highly versatile metabolic potential. In parallel, environmental genomics has provided glimpses into anaerobic methane oxidation by certain archaea, further supporting the hypothesis of reverse methanogenesis.
A marine microbial consortium apparently mediating anaerobic oxidation methane
Nature, 2000
A large fraction of globally produced methane is converted to CO 2 by anaerobic oxidation in marine sediments 1 . Strong geochemical evidence for net methane consumption in anoxic sediments is based on methane pro®les 2 , radiotracer experiments 3 and stable carbon isotope data 4 . But the elusive microorganisms mediating this reaction have not yet been isolated, and the pathway of anaerobic oxidation of methane is insuf®ciently understood. Recent data suggest that certain archaea reverse the process of methanogenesis by interaction with sulphate-reducing bacteria 5±7 . Here we provide microscopic evidence for a structured consortium of archaea and sulphate-reducing bacteria, which we identi®ed by¯uorescence in situ hybridization using speci®c 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 methanebased sulphate reduction, and apparently mediate anaerobic oxidation of methane.
Applied and Environmental Microbiology, 2000
Although abundant geochemical data indicate that anaerobic methane oxidation occurs in marine sediments, the linkage to specific microorganisms remains unclear. In order to examine processes of methane consumption and oxidation, sediment samples from mud volcanoes at two distinct sites on the Mediterranean Ridge were collected via the submersible Nautile. Geochemical data strongly indicate that methane is oxidized under anaerobic conditions, and compound-specific carbon isotope analyses indicate that this reaction is facilitated by a consortium of archaea and bacteria. Specifically, these methane-rich sediments contain high abundances of methanogen-specific biomarkers that are significantly depleted in 13 C (␦ 13 C values are as low as ؊95‰). Biomarkers inferred to derive from sulfate-reducing bacteria and other heterotrophic bacteria are similarly depleted. Consistent with previous work, such depletion can be explained by consumption of 13 Cdepleted methane by methanogens operating in reverse and as part a consortium of organisms in which sulfate serves as the terminal electron acceptor. Moreover, our results indicate that this process is widespread in Mediterranean mud volcanoes and in some localized settings is the predominant microbiological process.
Microbial methane turnover in different marine habitats
Palaeogeography, Palaeoclimatology, Palaeoecology, 2005
Microbial methanogenesis in the subsurface seafloor is responsible for the formation of large and dynamic gas reservoirs like the recently discovered gas hydrate deposits. Gas seepage occurs wherever methane builds up an overpressure outside the hydrate stability field, illustrating the potential importance of ocean margins for the global methane budget. However, a variety of bacteria and archaea are capable of methane consumption, and control the emission of methane to the hydrosphere. Unfortunately, much less is known about the microbial methane turnover in the ocean than about methane turnover in freshwater or terrestrial habitats. This investigation compares rates of methane production, anaerobic and aerobic methane oxidation at different marine sites, combining radiotracer (on-site) and in vitro measurements. Samples were obtained from gas hydrate bearing sediments, cold seeps, organic-rich and organic-poor subsurface sediments. All investigated subsurface sediments had the potential for methanogenesis as well as for methanotrophy. The anaerobic oxidation of methane (AOM) was highest in samples from gas hydrate areas and cold seeps. AOM was strongly influenced by methane partial pressure and temperature, indicating a substantial underestimation of in situ activity with current ex situ measuring techniques. A potential for aerobic methane oxidation was detected at all sites where the sediment had contact with oxic bottom water. A first comparison of methane turnover rates in diverse marine habitats showed that microbial methane oxidation provides a very effective barrier for methane emissions from the subsurface seafloor.
Multiple Groups of Methanotrophic Bacteria Mediate Methane Oxidation in Anoxic Lake Sediments
Frontiers in Microbiology, 2022
Freshwater lakes represent an important source of the potent greenhouse gas methane (CH 4) to the atmosphere. Methane emissions are regulated to large parts by aerobic (MOx) and anaerobic (AOM) oxidation of methane, which are important CH 4 sinks in lakes. In contrast to marine benthic environments, our knowledge about the modes of AOM and the related methanotrophic microorganisms in anoxic lake sediments is still rudimentary. Here, we demonstrate the occurrence of AOM in the anoxic sediments of Lake Sempach (Switzerland), with maximum in situ AOM rates observed within the surface sediment layers in presence of multiple groups of methanotrophic bacteria and various oxidants known to support AOM. However, substrate-amended incubations (with NO 2 − , NO 3 − , SO 4 2− , Fe-, and Mn-oxides) revealed that none of the electron acceptors previously reported to support AOM enhanced methane turnover in Lake Sempach sediments under anoxic conditions. In contrast, the addition of oxygen to the anoxic sediments resulted in an approximately 10-fold increase in methane oxidation relative to the anoxic incubations. Phylogenetic and isotopic evidence indicate that both Type I and Type II aerobic methanotrophs were growing on methane under both oxic and anoxic conditions, although methane assimilation rates were an order of magnitude higher under oxic conditions. While the anaerobic electron acceptor responsible for AOM could not be identified, these findings expand our understanding of the metabolic versatility of canonically aerobic methanotrophs under anoxic conditions, with important implications for future investigations to identify methane oxidation processes. Bacterial AOM by facultative aerobic methane oxidizers might be of much larger environmental significance in reducing methane emissions than previously thought.