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Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They belong to the domain Archaea and are members of the phylum Euryarchaeota. Methanogens are common in wetlands, where they are responsible for marsh gas, and can occur in the digestive tracts of animals including ruminants and humans, where they are responsible for the methane content of belching and flatulence. In marine sediments, the biological production of methane, termed methanogenesis, is generally confined to where sulfates are depleted below the top layers and methanogens play an indispensable role in anaerobic wastewater treatments. Other methanogens are extremophiles, found in environments such as hot springs and submarine hydrothermal vents as well as in the "solid" rock of Earth's crust, kilometers below the surface.
The Thermomicrobia is a group of thermophilic green non-sulfur bacteria. Based on species Thermomicrobium roseum and Sphaerobacter thermophilus, this bacteria class has the following description:
Sulfur-reducing bacteria are microorganisms able to reduce elemental sulfur (S0) to hydrogen sulfide (H2S). These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy and growth, in absence of oxygen. The final product of these processes, sulfide, has a considerable influence on the chemistry of the environment and, in addition, is used as electron donor for a large variety of microbial metabolisms. Several types of bacteria and many non-methanogenic archaea can reduce sulfur. Microbial sulfur reduction was already shown in early studies, which highlighted the first proof of S0 reduction in a vibrioid bacterium from mud, with sulfur as electron acceptor and H
2 as electron donor. The first pure cultured species of sulfur-reducing bacteria, Desulfuromonas acetoxidans, was discovered in 1976 and described by Pfennig Norbert and Biebel Hanno as an anaerobic sulfur-reducing and acetate-oxidizing bacterium, not able to reduce sulfate. Only few taxa are true sulfur-reducing bacteria, using sulfur reduction as the only or main catabolic reaction. Normally, they couple this reaction with the oxidation of acetate, succinate or other organic compounds. In general, sulfate-reducing bacteria are able to use both sulfate and elemental sulfur as electron acceptors. Thanks to its abundancy and thermodynamic stability, sulfate is the most studied electron acceptor for anaerobic respiration that involves sulfur compounds. Elemental sulfur, however, is very abundant and important, especially in deep-sea hydrothermal vents, hot springs and other extreme environments, making its isolation more difficult. Some bacteria – such as Proteus, Campylobacter, Pseudomonas and Salmonella – have the ability to reduce sulfur, but can also use oxygen and other terminal electron acceptors.
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.
In biology, syntrophy, synthrophy, or cross-feeding is the phenomenon of one species feeding on the metabolic products of another species to cope up with the energy limitations by electron transfer. In this type of biological interaction, metabolite transfer happens between two or more metabolically diverse microbial species that live in close proximity to each other. The growth of one partner depends on the nutrients, growth factors, or substrates provided by the other partner. Thus, syntrophism can be considered as an obligatory interdependency and a mutualistic metabolism between two different bacterial species.
Desulfobacter hydrogenophilus is a strictly anaerobic sulfate-reducing bacterium. It was isolated and characterized in 1987 by Friedrich Widdel of the University of Konstanz (Germany). Like most sulfate-reducing bacteria (SRB), D. hydrogenophilus is capable of completely oxidizing organic compounds (specifically acetate, pyruvate and ethanol) to CO2, and therefore plays a key role in biomineralization in anaerobic marine environments. However, unlike many SRB, D. hydrogenophilus is a facultative lithoautotroph, and can grow using H2 as an electron donor and CO2 as a carbon source. D. hydrogenophilus is also unique because it is psychrophilic (and has been shown to grow at temperatures as low as 0 °C or 32 °F). It is also diazotrophic, or capable of fixing nitrogen.
Syntrophobacter sulfatireducens is a species of bacteria notable for degrading propionate. It is notable for being syntrophic and for oxidising propionate. Its cells are egg-shaped. TB8106T is its type strain.
Syntrophomonas wolfei is a bacterium. It is anaerobic, syntrophic and fatty acid-oxidizing. It has a multilayered cell wall of the gram-negative type.
Thermacetogenium phaeum is a bacterium, the type species of its genus. It is strictly anaerobic, thermophilic, syntrophic and acetate-oxidizing. Its cells are gram-positive, endospore-forming and rod-shaped. Its type strain is PBT. It has a potential biotechnological role.
Clostridium uliginosum is a mesophilic bacterium oxidizing acetate in syntrophic association with a hydrogenotrophic methanogenic bacterium. It is a spore-forming, gram-positive, rod-shaped organism, with type strain BST. Its genome has been sequenced.
Methanococcus maripaludis is a species of methanogenic archaea found in marine environments, predominantly salt marshes. M. maripaludis is a weakly motile, non-spore-forming, Gram-negative, strict anaerobic mesophile with a pleomorphic coccoid-rod shape, averaging 1.2 by 1.6 μm is size. The genome of M. maripaludis has been sequenced, and over 1,700 protein-coding genes have been identified. In ideal conditions, M. maripaludis grows quickly and can double every two hours.
Syntrophomonas sapovorans is a bacterium. It is anaerobic, syntrophic, and fatty acid-oxidizing and obligately proton-reducing. Its type strain is OM. It has a doubling time of 40 hours. It is part of the family Syntrophomonadaceae based on comparative small-subunit (SSU) rRNA sequence analysis. This family currently contains three genera, Syntrophomonas, Syntrophospora, and Thermosyntropha, as well as two closely related isolates, strains FSM2 and FSS7.
Syntrophomonas palmitatica is a bacterium. It is anaerobic, syntrophic and fatty acid-oxidizing. Its type strain is GB8-1T. Cells are slightly curved, non-motile rods.
Syntrophomonas zehnderi is a bacterium. It is anaerobic, syntrophic and fatty acid-oxidizing. The type strain is OL-4T. Cells are slightly curved, non-motile rods.
"Syntrophothermus lipocalidus" is a bacterium, the type species and only currently described species in its genus. It is thermophilic, syntrophic, fatty-acid-oxidizing and anaerobic, and utilises isobutyrate. TGB-C1T is its type strain. Its genome has been fully sequenced.
Pelotomaculum thermopropionicum is an anaerobic, thermophilic, syntrophic propionate-oxidizing bacterium, the type species of its genus. The type strain is strain SI(T).
Syntrophobacter pfennigii is a species of syntrophic propionate-oxidising anaerobic bacterium. Strain KoProp1 is the type strain.
Smithella propionica is a species of bacteria, the type species of its genus. It is anaerobic, syntrophic, propionate-oxidizing bacteria, with type strain LYPT.
Thermosyntropha lipolytica is a lipolytic, anaerobic, alkalitolerant, thermophilic bacteria. It lives in syntrophic coculture with a methanogen. Its cells are non-motile, non-spore forming, straight or slightly curved rods. Its type strain is JW/VS-265T.
Syntrophothermus is a bacterial genus from the family of Syntrophomonadaceae. Up to now there is only on species of this genus known.
References
- ↑ Zhang, C. (2004). "Syntrophomonas curvata sp. nov., an anaerobe that degrades fatty acids in co-culture with methanogens". International Journal of Systematic and Evolutionary Microbiology. 54 (3): 969–973. doi: 10.1099/ijs.0.02903-0 . ISSN 1466-5026. PMID 15143051.
