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In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules and nutrients into organic matter using the oxidation of inorganic compounds or ferrous ions as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon from carbon dioxide through chemosynthesis, are phylogenetically diverse. Groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing gamma and epsilon proteobacteria, the Aquificae, the methanogenic archaea and the neutrophilic iron-oxidizing bacteria.
The purple sulfur bacteria (PSB) are part of a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in stratified water environments including hot springs, stagnant water bodies, as well as microbial mats in intertidal zones. Unlike plants, algae, and cyanobacteria, purple sulfur bacteria do not use water as their reducing agent, and therefore do not produce oxygen. Instead, they can use sulfur in the form of sulfide, or thiosulfate (as well, some species can use H2, Fe2+, or NO2−) as the electron donor in their photosynthetic pathways. The sulfur is oxidized to produce granules of elemental sulfur. This, in turn, may be oxidized to form sulfuric acid.
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 share a reaction center with green-sulfur bacteria.
Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria and purple non-sulfur bacteria (Rhodospirillaceae). Purple bacteria are anoxygenic phototrophs widely spread in nature, but especially in aquatic environments, where there are anoxic conditions that favor the synthesis of their pigments.
The Chromatiaceae are one of the two families of purple sulfur bacteria, together with the Ectothiorhodospiraceae. They belong to the order Chromatiales of the class Gammaproteobacteria, which is composed by unicellular Gram-negative organisms. Most of the species are photolithoautotrophs and conduct an anoxygenic photosynthesis, but there are also representatives capable of growing under dark and/or microaerobic conditions as either chemolithoautotrophs or chemoorganoheterotrophs.
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 or 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 H2 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 taxonomy, the Thermoplasmatales are an order of the Thermoplasmata. All are acidophiles, growing optimally at pH below 2. Picrophilus is currently the most acidophilic of all known organisms, being capable of growing at a pH of -0.06. Many of these organisms do not contain a cell wall, although this is not true in the case of Picrophilus. Most members of the Thermotoplasmata are thermophilic.
Spirillum is a genus of Gram-negative bacteria in the family Spirillaceae of the Nitrosomonadales of the Betaproteobacteria. There are two species of Spirillum with validly or effectively published names - Spirillum winogradskyi and Spirillum volutans.
In the taxonomy of microorganisms, the Methanomicrobia are a class of the Euryarchaeota.
In taxonomy, the Methanopyrales are an order of microbes within the class methanopyri.
In taxonomy, the Thermococcales are an order of microbes within the Thermococci. The species within the Thermococcales are used in laboratories as model organisms. All these species are strict anaerobes and can ferment sugars as sources of carbon, but they also need elemental sulfur.
In taxonomy, the Methanopyraceae are a family of the Methanopyrales. This family contains only one genus, which contains only one species, Methanopyrus kandleri. It is chemolitoautotrophic and its cells are bar-shaped. It can grow comfortably at a temperature of 98 °C and can survive at temperatures as high as 110 °C, making it the most thermophilic known methanogen. It has been found to live in hydrothermal vents.
In taxonomy, the Methanosaetaceae are a family of microbes within the order Methanosarcinales. All species within this family use acetate as their sole source of energy.
In taxonomy, Rhodothalassium is a genus of the Rhodobacteraceae. Up to now there is only one species of this genus known.
Rhodovulum sulfidophilum is a purple bacteria. The cells are rod-shaped, 0.6 to 0.9 μ wide and 0.9 to 2.0 μ long, and motile by means of polar flagella. Cell division occurs by binary fission. Its pigments consist of bacteriochlorophyll a and of carotenoids, most probably of the spheroidene group. The new species needs 2.5% (w/v) sodium chloride for optimal growth. The bacteria has a high sulfide tolerance. Sulfide and thiosulfate are oxidized to sulfate without an intermediate accumulation of elemental sulfur. It can either grow photoautotrophically or photoheterotrophically.
Rhodocyclus purpureus is a species of bacteria. Its cells are half-ring-shaped and ring-shaped before cell division; the half-rings being 0.6 to 0.7 μm wide and 2.5 to 3.0 μm long. Open or compact coils of variable length are also formed. It is facultatively aerobic and its type strain is “Ames” 6770.
Thiorhodospira sibirica is a species of alkaliphilic purple sulfur bacterium. It is strictly anaerobic, vibrioid- or spiral-shaped and motile by means of a polar tuft of flagella.
Phenylobacterium immobile is an aerobic, gram-negative, rod or coccoid-shaped bacteria that is non-motile and non-spore-forming. It is notable for degrading Chloridazon. Its type strain is E.
Nocardioides aquaticus is a species of Gram-positive, non-motile and aerobic bacteria. Its type strain is EL-17KT.
Deinococcus indicus is a species of arsenic-resistant bacterium. It is Gram-negative, rod-shaped, non-motile, non-sporulating and red-pigmented, with type strain Wt/1aT.
References
- ↑ Overmann, Jörg; Fischer, Ulrich; Pfennig, Norbert (1992). "A new purple sulfur bacterium from saline littoral sediments, Thiorhodovibrio winogradskyi gen. nov. and sp. nov". Archives of Microbiology. 157 (4): 329–335. doi:10.1007/BF00248677. ISSN 0302-8933. S2CID 13151519.
