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.
In biology, syntrophy, syntrophism, or cross-feeding is the cooperative interaction between at least two microbial species to degrade a single substrate. This type of biological interaction typically involves the transfer of one or more metabolic intermediates between two or more metabolically diverse microbial species living in close proximity to each other. Thus, syntrophy can be considered an obligatory interdependency and a mutualistic metabolism between different microbial species, wherein the growth of one partner depends on the nutrients, growth factors, or substrates provided by the other(s).
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.
Clostridium phytofermentans is an obligately anaerobic rod-shaped spore-forming, Gram-positive bacterium in the family Lachnospiraceae. It is a model organism of interest for its ability to ferment diverse plant polysaccharides including cellulose, hemicellulose, and pectin to ethanol, acetate, and hydrogen. The C. phytofermentans 4.8 Mb genome has been fully sequenced, revealing it contains over 170 enzymes in the CAZy database, though one hydrolase appears to be essential for degrading cellulose.
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.
Methanothrix soehngenii is a species of methanogenic archaea. Its cells are non-motile, non-spore-forming, rod-shaped and are normally combined end to end in long filaments, surrounded by a sheath-like structure. It is named in honour of N. L. Söhngen.
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.
Methanococcus maripaludis is a species of methanogenic archaea found in marine environments, predominantly salt marshes. M. maripaludis is a non-pathogenic, gram-negative, weakly motile, non-spore-forming, and strictly anaerobic mesophile. It is classified as a chemolithoautotroph. This archaeon has a pleomorphic coccoid-rod shape of 1.2 by 1.6 μm, in average size, and has many unique metabolic processes that aid in survival. M. maripaludis also has a sequenced genome consisting of around 1.7 Mbp with over 1,700 identified protein-coding genes. 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 curvata is a bacterium. It is anaerobic, syntrophic and fatty acid-oxidizing. Its type strain is GB8-1T.
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.
Syntrophobacter fumaroxidans is a species of syntrophic propionate-degrading sulfate-reducing bacterium. Strain MPOBT is the type strain. Its genome has been fully sequenced.
"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).
Clostridium autoethanogenum is an anaerobic bacterium that produces ethanol from carbon monoxide, in so-called syngas fermentation, being one of the few known microorganisms to do so. It is gram-positive, spore-forming, rod-like, motile, and was first isolated from rabbit feces. Its type strain is strain JA1-1. Its genome has been sequenced and the genes required for utilising carbon monoxide as a sole carbon and energy source have been determined.
Syntrophaceticus schinkii is a species of strictly anaerobic, mesophilic, endospore-forming, syntrophic, acetate-oxidizing bacterium, the type species of its genus. Its type strain is Sp3T, which was isolated from an anaerobic filter treating wastewater in a fishmeal factory.
Desulfovibrio alcoholivorans is a bacterium from the genus of Desulfovibrio which has been isolated from alcohol industry waste water in France.
Tepidanaerobacter is a genus of anaerobic, moderately thermophilic, syntrophic bacteria from the family Tepidanaerobacteraceae.
Tepidanaerobacter acetatoxydans is an anaerobic bacterium from the genus of Tepidanaerobacter.
