The green sulfur bacteria are a phylum, Chlorobiota, of obligately anaerobic photoautotrophic bacteria that metabolize sulfur.
The purple sulfur bacteria (PSB) are part of a group of Pseudomonadota 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.
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. 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 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.
Gammaproteobacteria is a class of bacteria in the phylum Pseudomonadota. It contains about 250 genera, which makes it the most genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scientifically important groups of bacteria belong to this class. All members of this class are Gram-negative. It is the most phylogenetically and physiologically diverse class of the Pseudomonadota.
Rhodopseudomonas palustris is a rod-shaped, Gram-negative purple nonsulfur bacterium, notable for its ability to switch between four different modes of metabolism.
The Sippewissett microbial mat is a microbial mat in the Sippewissett Salt Marsh located along the lower eastern Buzzards Bay shoreline of Cape Cod, about 5 miles north of Woods Hole and 1 mile southwest of West Falmouth, Massachusetts, in the United States. The marsh has two regions, the Great Sippewisset Marsh to the north and Little Sippewisset Marsh to the south, separated from each other by a narrow tongue of land. The marsh extends into an estuary in which the intertidal zone provides a dynamic environment that supports a diverse ecology, including threatened and endangered species such as the roseate tern. The ecology of the salt marsh is based in and supported by the microbial mats which cover the ground of the marsh.
Rhodovulum sulfidophilum is a gram-negative purple nonsulfur bacteria. The cells are rod-shaped, and range in size from 0.6 to 0.9 μm wide and 0.9 to 2.0 μm long, and have a polar flagella. These cells reproduce asexually by binary fission. This bacterium can grow anaerobically when light is present, or aerobically (chemoheterotrophic) under dark conditions. It contains the photosynthetic pigments bacteriochlorophyll a and of carotenoids.
Rhodoblastus acidophilus, formerly known as Rhodopseudomonas acidophila, is a gram-negative purple non-sulfur bacteria. The cells are rod-shaped or ovoid, 1.0 to 1.3 μm wide and 2 to 5 μm long. They are motile by means of polar flagella, and they multiply by budding. The photopigments consist of bacteriochlorophyll a and carotenoids of the spirilloxanthin series. All strains can grow either under anaerobic conditions in the light or under microaerophilic to aerobic conditions in the dark.
Chlorobium chlorochromatii, originally known as Chlorobium aggregatum, is a symbiotic green sulfur bacteria that performs anoxygenic photosynthesis and functions as an obligate photoautotroph using reduced sulfur species as electron donors. Chlorobium chlorochromatii can be found in stratified freshwater lakes.
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.
Rhodobacter capsulatus is a species of purple bacteria, a group of bacteria that can obtain energy through photosynthesis. Its name is derived from the Latin adjective "capsulatus", itself derived Latin noun "capsula", and the associated Latin suffix for masculine nouns, "-atus".
Marichromatium is a genus in the phylum Pseudomonadota (Bacteria). The name Marichromatium derives from: Latin mare, the sea; Neo-Latin Chromatium, a genus name; to give Marichromatium, the Chromatium of the sea, the truly marine Chromatium.
Halorhodospira neutriphila is a bacterium from the genus of Halorhodospira which has been isolated from a microbial mat from a marine saltern from Rhone Delta in France. The microbial mat forms at the sediment surface and is between 10 and 20 mm thick, below a fine layer (2–3 cm) of gypsum crust. The mat is composed of a red layer of purple bacteria strains below a green layer of cyanobacteria, interspersed with sulfur globules, and occasionally covered by halite deposits. These mat forming microbes live in anoxic muds and sediments and form a benthic mat in a hypersaline lagoon environment where the salinity of the water ranges from 240-320‰ of total salinity. H. neutriphila was isolated from the red layer of the microbial layer and found to be extremely halophilic and well adapted to withstand the extreme saline conditions of their modified marine habitat. The type strain was identified as strain SG 3301T.
Thioalkalicoccus is a Gram-negative, mesophilic and obligate alkaliphilic genus of bacteria from the family of Chromatiaceae with one known species. Thioalkalicoccus limnaeus occurs in brackish water lakes.
Thiococcus is a Gram-negative, non‐motile, obligately phototrophic and strictly anaerobic genus of bacteria from the family of Chromatiaceae with one known species. Thiococcus pfennigii was first isolated from salt marshes.
Thiodictyon is a genus of gram-negative bacterium classified within purple sulfur bacteria (PSB).
Chloroflexus aggregans is a bacterium from the genus Chloroflexus which has been isolated from hot springs in Japan.
Prosthecochloris aestuarii is a green sulfur bacterium in the genus Prosthecochloris. This organism was originally isolated from brackish lagoons located in Sasyk-Sivash and Sivash. They are characterized by the presence of "prosthecae" on their cell surface; the inner part of these appendages house the photosynthetic machinery within chlorosomes, which are characteristic structures of green sulfur bacteria. Additionally, like other green sulfur bacteria, they are Gram-negative, non-motile, and non-spore forming. Of the four major groups of green sulfur bacteria, P. aestuarii serves as the type species for Group 4.
