Sulfur-reducing bacteria
[1] These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy and growth, in absence of oxygen.
[2] 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.
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.
[2] 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.
[2][7][8][9][10][1] Several types of sulfur-reducing bacteria have been discovered in different habitats like deep and shallow sea hydrothermal vents, freshwater, volcanic acidic hot springs and others.
Other phyla that present sulfur-reducing bacteria are: Bacillota (Desulfitobacterium, Ammonifex, and Carboxydothermus), Aquificota (Desulfurobacterium and Aquifex), Synergistota (Dethiosulfovibrio), Deferribacterota (Geovibrio), Thermodesulfobacteriota, Spirochaetota, and Chrysiogenota.
[1][2] Persephonella (guaimasensis, marina), Thermocrinis (ruber), Thermosulfidibacter (takaii), Thermovibrio (ammonificans, guaymasensis, ruber) Desulfitibacter (alkalitolerans), Desulfitispora (alkaliphila), Desulfitobacterium (hafniense, chlororespirans, dehalogenans, metallireducens), Desulfosporosinus (acididurans, acidiphilus, orientis, meridiei, auripigmenti), Desulfotomaculum (thermosubterraneus, salinum, geothermicum, reducens, intricatum), Ercella (succinogenes), Halanaerobium (congolense), Halarsenatibacter (silvermanii), Sporanaerobacter (acetigenes), Thermoanaerobacter (sulfurophilus) Desulfomonile (tiedjei), Desulfonatronovibrio (thiodismutans), Desulfonatronum (thioautotrophicum), Desulfovermiculus (halophilus), Desulfovibrio, Desulfurella, Desulfurivibrio (alkaliphilus), Desulfuromonas, Desulfuromusa, Geoalkalibacter (subterraneus), Geobacter, Hippea (maritima), Pelobacter Caldimicrobium (exile), Thermodesulfobacterium (geofontis) Thioreductor (incertae sedis), Wolinella (succinogenes) Thermanaerovibrio (acidaminovorans, velox), Thermovirga (lienii), Mesotoga (infera, prima), Petrotoga (mexicana, miotherma, mobilis), Thermosipho (aficanus), Thermotoga (lettingae, maritima, naphthophila, neapolitana), Pelobacter Nautilia, Nitratiruptor, Sulfurimonas, Sulfurospirillum, Sulfurovum, Wolinella Sulfur reduction metabolism is an ancient process, found in the deep branches of the phylogenetic tree.
This metabolism is largely present in extreme environments where, especially in recent years, many microorganisms have been isolated, bringing new and important data on the subject.
[21] Acidithiobacillus ferrooxidans is abundant in natural environments associated with pyritic ore bodies, coal deposits, and their acidified drainages.
The first description of the species was provided in 1931, Shewanella putrefaciens, a non-fermentative bacilli with a single polar flagellum which grow well on conventional solid media.
Obligately anaerobic, moderate thermophilic, they generally occur in warm sediments and in thermally heated cyanobacterial or bacterial communities that are rich in organic compounds and elemental sulfur.
[33] The phylum Campylobacterota presents many sulfur-oxidizing known species, that have been recently recognized as able to reduce elemental sulfur, in some cases also preferring this pathway, coupled with hydrogen oxidation.
[1] Sulfurimonas species were previously considered to be chemolithoautotrophic sulfur-oxidizing bacteria (SOB), and there were only genetic evidences supporting a possible sulfur-reducing metabolism, but now it has been shown that sulfur reduction also occurs in this genus.
In particular the presence of both a cytoplasmic and a periplasmic polysulfide reductases has been detected, in order to reduce cyclooctasulfur, which is the most common form of elemental sulfur in vent environments.
[36] Nautilia species are anaerobic, neutrophile, thermophilic sulfur-reducing bacteria, first discovered and isolated from a polychaete worm inhabiting deep sea hydrothermal vents, Alvinella pompejana.
[43] Thermovibrio ammonificans[36] is a gram-negative sulfur reducing bacteria, found in deep sea hydrothermal vent chimney.
It is a chemolithoautotroph that grows in the presence of H2 and CO2, using nitrate or elemental sulfur as electron acceptors with concomitant formation of ammonium or hydrogen sulfide, respectively.
They are strictly anaerobes and fermenters, catabolizing sugars or starch and producing lactate, acetate, CO2, and H2 as products,[1] and can grow in a range temperature of 48–90 °C.
is widely used as a model for studying adaptation to high temperatures, microbial evolution and biotechnological opportunities, such as biohydrogen production and biocatalysis.
[9] In some communities found in hydrothermal vents, their proliferation is enhanced thanks to the reactions carried out by thermophilic photo- or chemoautotrophs, in which there is simultaneously production of elemental sulfur and organic matter, respectively electron acceptor and energy source for sulfur-reducing bacteria.
This association of micro-organisms inhabits sulfide-rich habitats, where the chemical oxidation of sulfide by oxygen, manganese or ferric iron or by the activity of sulfide-oxidizing bacteria results in the formation of thiosulfate or elemental sulfur.
[65] The majority of sulfur on Earth is present in sediments and rocks, but its quantity in the oceans represents the primary reservoir of sulfate of the entire biosphere.
Human activities such as burning fossil fuels, also contribute to the cycle by entering a significant amount of sulfur dioxide in the atmosphere.
For example, these type of bacteria can be used in to generate hydrogen sulfide in order to obtain the selective precipitation and recovery of heavy metals in metallurgical and mining industries.
The first in which biological sulfur reduction occurs, the second through which dissolved H2S in wastewaters is stripped into hydrogen sulfide gas, and the third consists in the treatment of flue gases, removing over 90% of SO2 and NO, according to this study.
The sulfidogenic process driven by sulfur reducing bacteria (Desulfurella) take place under acid condition and produce sulfide with which arsenite precipitates.
Microbial sulfur reduction also produces protons that lower the pH in arsenic-contaminated water and prevent the formation of thioarsenite by-production with sulfide.
[70] Wastewater deriving from industries that work on chloralkali and battery production, contains high levels of mercury ions, threatening aquatic ecosystems.
[71] Recent studies demonstrate that sulfidogenic process by sulfur reducing bacteria can be a good technology in the treatment of mercury-contaminate waters.
