Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
Methanogens are anaerobic archaea that produce methane as a byproduct of their energy metabolism, i.e., catabolism. Methane production, or methanogenesis, is the only biochemical pathway for ATP generation in methanogens. All known methanogens belong exclusively to the domain Archaea, although some bacteria, plants, and animal cells are also known to produce methane. However, the biochemical pathway for methane production in these organisms differs from that in methanogens and does not contribute to ATP formation. Methanogens belong to various phyla within the domain Archaea. Previous studies placed all known methanogens into the superphylum Euryarchaeota. However, recent phylogenomic data have led to their reclassification into several different phyla. Methanogens are common in various anoxic environments, such as marine and freshwater sediments, wetlands, the digestive tracts of animals, wastewater treatment plants, rice paddy soil, and landfills. While some methanogens are extremophiles, such as Methanopyrus kandleri, which grows between 84 and 110°C, or Methanonatronarchaeum thermophilum, which grows at a pH range of 8.2 to 10.2 and a Na+ concentration of 3 to 4.8 M, most of the isolates are mesophilic and grow around neutral pH.
Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In anoxic environments, it is the final step in the decomposition of biomass. Methanogenesis is responsible for significant amounts of natural gas accumulations, the remainder being thermogenic.
Anammox, an abbreviation for "anaerobic ammonium oxidation", is a globally important microbial process of the nitrogen cycle that takes place in many natural environments. The bacteria mediating this process were identified in 1999, and were a great surprise for the scientific community. In the anammox reaction, nitrite and ammonium ions are converted directly into diatomic nitrogen and water.
Methanotrophs are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to survive.
"Candidatus Brocadia anammoxidans" is a bacterial member of the phylum Planctomycetota and therefore lacks peptidoglycan in its cell wall, and has a compartmentalized cytoplasm.
Denitrifying bacteria are a diverse group of bacteria that encompass many different phyla. This group of bacteria, together with denitrifying fungi and archaea, is capable of performing denitrification as part of the nitrogen cycle. Denitrification is performed by a variety of denitrifying bacteria that are widely distributed in soils and sediments and that use oxidized nitrogen compounds such as nitrate and nitrite in the absence of oxygen as a terminal electron acceptor. They metabolize nitrogenous compounds using various enzymes, including nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (NOS), turning nitrogen oxides back to nitrogen gas or nitrous oxide.
Methanosarcina is a genus of euryarchaeote archaea that produce methane. These single-celled organisms are known as anaerobic methanogens that produce methane using all three metabolic pathways for methanogenesis. They live in diverse environments where they can remain safe from the effects of oxygen, whether on the earth's surface, in groundwater, in deep sea vents, and in animal digestive tracts. Methanosarcina grow in colonies.
Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.
Methanobacterium is a genus of the Methanobacteria class in the Archaea kingdom, which produce methane as a metabolic byproduct. Despite the name, this genus belongs not to the bacterial domain but the archaeal domain. Methanobacterium are nonmotile and live without oxygen, which is toxic to them, and they only inhabit anoxic environments.
Anaerobic oxidation of methane (AOM) is a methane-consuming microbial process occurring in anoxic marine and freshwater sediments. AOM is known to occur among mesophiles, but also in psychrophiles, thermophiles, halophiles, acidophiles, and alkophiles. During AOM, methane is oxidized with different terminal electron acceptors such as sulfate, nitrate, nitrite and metals, either alone or in syntrophy with a partner organism.
Archaea is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotic. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.
Greenhouse gas emissions from wetlands of concern consist primarily of methane and nitrous oxide emissions. Wetlands are the largest natural source of atmospheric methane in the world, and are therefore a major area of concern with respect to climate change. Wetlands account for approximately 20–30% of atmospheric methane through emissions from soils and plants, and contribute an approximate average of 161 Tg of methane to the atmosphere per year.
F430 is the cofactor (sometimes called the coenzyme) of the enzyme methyl coenzyme M reductase (MCR). MCR catalyzes the reaction EC 2.8.4.1 that releases methane in the final step of methanogenesis:
In the taxonomy of microorganisms, the Methanothrix is a genus of methanogenic archaea within the Euryarchaeota. Methanothrix cells were first isolated from a mesophilic sewage digester but have since been found in many anaerobic and aerobic environments. Methanothrix were originally understood to be obligate anaerobes that can survive exposure to high concentrations of oxygen, but recent studies have shown at least one Candidatus operational taxonomic unit proposed to be in the Methanothrix genus not only survives but remains active in oxic soils. This proposed species, Ca. Methanothrix paradoxum, is frequently found in methane-releasing ecosystems and is the dominant methanogen in oxic soils.
Hadesarchaea, formerly called the South-African Gold Mine Miscellaneous Euryarchaeal Group, are a class of thermophile microorganisms that have been found in deep mines, hot springs, marine sediments, and other subterranean environments.
The sulfate-methane transition zone (SMTZ) is a zone in oceans, lakes, and rivers typically found below the sediment surface in which sulfate and methane coexist. The formation of a SMTZ is driven by the diffusion of sulfate down the sediment column and the diffusion of methane up the sediments. At the SMTZ, their diffusion profiles meet and sulfate and methane react with one another, which allows the SMTZ to harbor a unique microbial community whose main form of metabolism is anaerobic oxidation of methane (AOM). The presence of AOM marks the transition from dissimilatory sulfate reduction to methanogenesis as the main metabolism utilized by organisms.
The hydrothermal vent microbial community includes all unicellular organisms that live and reproduce in a chemically distinct area around hydrothermal vents. These include organisms in the microbial mat, free floating cells, or bacteria in an endosymbiotic relationship with animals. Chemolithoautotrophic bacteria derive nutrients and energy from the geological activity at Hydrothermal vents to fix carbon into organic forms. Viruses are also a part of the hydrothermal vent microbial community and their influence on the microbial ecology in these ecosystems is a burgeoning field of research.
NC10 is a bacterial phylum with candidate status, meaning its members remain uncultured to date. The difficulty in producing lab cultures may be linked to low growth rates and other limiting growth factors.
Candidatus "Methylomirabilis oxyfera" is a candidate species of Gram-negative bacteria belonging to the NC10 phylum, characterized for its capacity to couple anaerobic methane oxidation with nitrite reduction in anoxic environments. To acquire oxygen for methane oxidation, M. oxyfera utilizes an intra-aerobic pathway through the reduction of nitrite (NO2) to dinitrogen (N2) and oxygen.
