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Heliobacteria are a unique subset of prokaryotic bacteria that process light for energy. Distinguishable from other phototrophic bacteria, they utilize a unique photosynthetic pigment, bacteriochlorophyll g and are the only known Gram-positive phototroph. They are a key player in symbiotic nitrogen fixation alongside plants, and use a type I reaction center like green-sulfur bacteria.
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.
Beggiatoa is a genus of Gammaproteobacteria belonging to the order Thiotrichales, in the Pseudomonadota phylum. This genus was one of the first bacteria discovered by Ukrainian botanist Sergei Winogradsky. During his research in Anton de Bary's laboratory of botany in 1887, he found that Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source, forming intracellular sulfur droplets, with oxygen as the terminal electron acceptor and CO2 used as a carbon source. Winogradsky named it in honor of the Italian doctor and botanist Francesco Secondo Beggiato (1806 - 1883), from Venice. Winogradsky referred to this form of metabolism as "inorgoxidation" (oxidation of inorganic compounds), today called chemolithotrophy. These organisms live in sulfur-rich environments such as soil, both marine and freshwater, in the deep sea hydrothermal vents and in polluted marine environments. The finding represented the first discovery of lithotrophy. Two species of Beggiatoa have been formally described: the type species Beggiatoa alba and Beggiatoa leptomitoformis, the latter of which was only published in 2017. This colorless and filamentous bacterium, sometimes in association with other sulfur bacteria (for example the genus Thiothrix), can be arranged in biofilm visible to the naked eye formed by a very long white filamentous mat, the white color is due to the stored sulfur. Species of Beggiatoa have cells up to 200 µm in diameter and they are one of the largest prokaryotes on Earth.
Hydrogenobacter thermophilus is an extremely thermophilic, straight rod (bacillus) bacterium. TK-6 is the type strain for this species. It is a Gram negative, non-motile, obligate chemolithoautotroph. It belongs to one of the earliest branching order of Bacteria. H. thermophilus TK-6 lives in soil that contains hot water. It was one of the first hydrogen oxidizing bacteria described leading to the discovery, and subsequent examination of many unique proteins involved in its metabolism. Its discovery contradicted the idea that no obligate hydrogen oxidizing bacteria existed, leading to a new understanding of this physiological group. Additionally, H. thermophilus contains a fatty acid composition that had not been observed before.
A soda lake or alkaline lake is a lake on the strongly alkaline side of neutrality, typically with a pH value between 9 and 12. They are characterized by high concentrations of carbonate salts, typically sodium carbonate, giving rise to their alkalinity. In addition, many soda lakes also contain high concentrations of sodium chloride and other dissolved salts, making them saline or hypersaline lakes as well. High pH and salinity often coincide, because of how soda lakes develop. The resulting hypersaline and highly alkalic soda lakes are considered some of the most extreme aquatic environments on Earth.
Desulfonatronovibrio hydrogenovorans is a bacterium, the type species of its genus. It is an alkaliphilic, sulfate-reducing and motile bacterium. It is obligately sodium-dependent and its type strain is Z-7935.
Thiomicrospira aerophila is an obligately alkaliphilic and obligately chemolithoautotrophic sulfur-oxidizing bacterium that was previously the type species of Thioalkalimicrobium prior to reclassification in 2017. It was first isolated from soda lakes in northern Russia.
Thiomicrospira siberica is a species of obligately alkaliphilic and obligately chemolithoautotrophic sulfur-oxidizing bacteria. It was first isolated from soda lakes in northern Russia, hence the specific epithet. In 2017, all 4 species of the genus Thioalkalimicrobium were reclassified to Thiomicrospira.
Thioalkalivibrio versutus is an obligately alkaliphilic and obligately chemolithoautotrophic sulfur-oxidizing bacteria. It was first isolated from soda lakes in northern Russia.
Thioalkalivibrio nitratis is an obligately alkaliphilic and obligately chemolithoautotrophic sulfur-oxidizing bacteria. It was first isolated from soda lakes in northern Russia.
Thioalkalivibrio denitrificancs is an obligately alkaliphilic and obligately chemolithoautotrophic sulfur-oxidizing bacteria. It was first isolated from soda lakes in northern Russia.
Thioalkalivibrio thiocyanoxidans is a species of alkaliphilic and obligately autotrophic sulfur-oxidizing bacterium. It was first isolated from soda lakes. Its type strain is Arh 2.
Desulfobacter curvatus is a sulfate-reducing bacteria, with type strain AcRM3.
Thioalkalivibrio is a Gram-negative, mostly halophilic bacterial genus of the family Ectothiorhodospiraceae.
Thioalkalimicrobium is a defunct bacterial genus within the Gammaproteobacteria. All 4 species in the genus were reclassified to the genus Thiomicrospira in 2017.
Alkalibacter saccharofermentans is a Gram-positive, obligately anaerobic, alkaliphilic and non-spore-forming bacterium from the genus of Alkalibacter which has been isolated from a soda lake in the Transbaikal regio in Russia.
Acetivibrio alkalicellulosi is an obligately alkaliphilic and anaerobic bacterium from the genus Acetivibrio which has been isolated from sediments of the Beloe soda lake from Buryatiya in Russia.
The Thioalkalibacteraceae are a family of extremophiles, namely halophilic, alkaliphilic or alkalitolerant, mesophilic to thermophilic obligately chemolithoautotrophic organisms in the Chromatiales comprising the genus Thioalkalibacter and Guyparkeria. The family is closely related to the family Halothiobacillaceae of halotolerant, mesophilic obligate autotrophs.
Natronoflexus is an obligately anaerobic and alkaliphilic genus of bacteria from the family of Marinilabiliaceae with one known species. Natronoflexus pectinivorans has been isolated from sediments from a soda lake from Altai in Russia.
Ann Patricia Wood is a retired British biochemist and bacteriologist who specialized in the ecology, taxonomy and physiology of sulfur-oxidizing chemolithoautotrophic bacteria and how methylotrophic bacteria play a role in the degradation of odour causing compounds in the human mouth, vagina and skin. The bacterial genus Annwoodia was named to honor her contributions to microbial research in 2017.
References
- ↑ Sorokin DY, Tourova TP, Lysenko AM, Mityushina LL, Kuenen JG (2002). "Thioalkalivibrio thiocyanoxidans sp. nov. and Thioalkalivibrio paradoxus sp. nov., novel alkaliphilic, obligately autotrophic, sulfur-oxidizing bacteria capable of growth on thiocyanate, from soda lakes". Int J Syst Evol Microbiol. 52 (Pt 2): 657–64. doi: 10.1099/00207713-52-2-657 . PMID 11931180.
