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.
Thermithiobacillus tepidarius is a member of the Acidithiobacillia isolated from the thermal groundwaters of the Roman Baths at Bath, Somerset, United Kingdom. It was previously placed in the genus Thiobacillus. The organism is a moderate thermophile, 43–45 °C (109–113 °F), and an obligate aerobic chemolithotrophic autotroph. Despite having an optimum pH of 6.0–7.5, growth can continue to an acid medium of pH 4.8. Growth can only occur on reduced inorganic sulfur compounds and elementary sulfur, but unlike some species in other genus of the same family, Acidithiobacillus, Thermithiobacillus spp. are unable to oxidise ferrous iron or iron-containing minerals.
Rhodopila globiformis is a species of bacteria, formerly known as Rhodopseudomonas globiformis. It is a motile, spherical organism. Cells can grow between 1.6 and 1.8 μm in diameter. The photopigments consist of bacteriochlorophyll aP and aliphatic methoxylated ketocarotenoids. The organism grows under anaerobic conditions in the light or under microaerophilic conditions in the dark. Biotin, p-aminobenzoic acid and a source of reduced sulfur are required as growth factors in order to cultivate this bacteria. This bacteria possesses a high potential cytochrome c2.
Desulfuromonas acetoxidans is a species of bacteria. It is strictly anaerobic, rod-shaped, laterally flagellated and Gram-negative. It is unable to ferment organic substances; it obtains energy for growth by anaerobic sulfur respiration.
Desulfobulbus propionicus is a Gram-negative, anaerobic chemoorganotroph. Three separate strains have been identified: 1pr3T, 2pr4, and 3pr10. It is also the first pure culture example of successful disproportionation of elemental sulfur to sulfate and sulfide. Desulfobulbus propionicus has the potential to produce free energy and chemical products.
Chlorobaculum tepidum, previously known as Chlorobium tepidum, is an anaerobic, thermophilic green sulfur bacteria first isolated from New Zealand. Its cells are gram-negative and non-motile rods of variable length. They contain chlorosomes and bacteriochlorophyll a and c.
Acidithiobacillus caldus formerly belonged to the genus Thiobacillus prior to 2000, when it was reclassified along with a number of other bacterial species into one of three new genera that better categorize sulfur-oxidizing acidophiles. As a member of the Gammaproteobacteria class of Pseudomonadota, A. caldus may be identified as a Gram-negative bacterium that is frequently found in pairs. Considered to be one of the most common microbes involved in biomining, it is capable of oxidizing reduced inorganic sulfur compounds (RISCs) that form during the breakdown of sulfide minerals. The meaning of the prefix acidi- in the name Acidithiobacillus comes from the Latin word acidus, signifying that members of this genus love a sour, acidic environment. Thio is derived from the Greek word thios and describes the use of sulfur as an energy source, and bacillus describes the shape of these microorganisms, which are small rods. The species name, caldus, is derived from the Latin word for warm or hot, denoting this species' love of a warm environment.
Pelobacter propionicus is a species of bacteria that ferments 2,3-butanediol and acetoin. It is Gram-negative, strictly anaerobic and non-spore-forming. Ott Bd 1 is the type strain.
Desulfovibrio oxyclinae is a bacterium. It is sulfate-reducing, and was first isolated from the upper 3mm layer of a hypersaline cyanobacterial mat in Sinai.
Holophaga foetida is a bacterium, the type species of its genus. It is a homoacetogenic bacterium degrading methoxylated aromatic compounds. It is gram-negative, obligately anaerobic and rod-shaped, with type strain TMBS4. Its genome has been sequenced. It is known for its ability to anaerobically degrade aromatic compounds and the production of volatile sulfur compounds through a unique pathway.
Desulfobacterium catecholicum is a catechol-degrading lemon-shaped non-sporing sulfate-reducing bacterium. Its type strain is Nzva20.
Desulfurella acetivorans is a thermophilic acetate-oxidizing sulfur-reducing eubacterium. It is Gram-negative, short rod-shaped, motile, with a single polar flagellum.
Desulfocapsa thiozymogenes is an anaerobic, gram-negative bacterium. It disproportionates elemental sulfur. It is the type species of its genus.
Thiorhodovibrio winogradskyi is a purple sulfur bacteria, the type species of its genus. Its cells are vibrioid-to spirilloid-shaped and motile by means of single polar flagella. It is moderately halophilic, with type strain SSP1.
Desulfovibrio alcoholivorans is a bacterium from the genus of Desulfovibrio which has been isolated from alcohol industry waste water in France.
The genus Annwoodia was named in 2017 to circumscribe an organism previously described as a member of the genus Thiobacillus, Thiobacillus aquaesulis - the type and only species is Annwoodia aquaesulis, which was isolated from the geothermal waters of the Roman Baths in the city of Bath in the United Kingdom by Ann P. Wood and Donovan P. Kelly of the University of Warwick - the genus was subsequently named to honour Wood's contribution to microbiology. The genus falls within the family Thiobacillaceae along with Thiobacillus and Sulfuritortus, both of which comprise autotrophic organisms dependent on thiosulfate, other sulfur oxyanions and sulfide as electron donors for chemolithoheterotrophic growth. Whilst Annwoodia spp. and Sulfuritortus spp. are thermophilic, Thiobacillus spp. are mesophilic.
Microbial oxidation of sulfur is the oxidation of sulfur by microorganisms to build their structural components. The oxidation of inorganic compounds is the strategy primarily used by chemolithotrophic microorganisms to obtain energy to survive, grow and reproduce. Some inorganic forms of reduced sulfur, mainly sulfide (H2S/HS−) and elemental sulfur (S0), can be oxidized by chemolithotrophic sulfur-oxidizing prokaryotes, usually coupled to the reduction of oxygen (O2) or nitrate (NO3−). Anaerobic sulfur oxidizers include photolithoautotrophs that obtain their energy from sunlight, hydrogen from sulfide, and carbon from carbon dioxide (CO2).
Trithionate is an oxyanion of sulfur with the chemical formula S
3O2−
6. It is the conjugate base of trithionic acid. Dilute sodium hydroxide hydrolyzes S
4N
4 as follows, yielding sodium thiosulfate and sodium trithionate:
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.
