Sulfate-reducing microorganism

Desulfovibrio vulgaris is the best-studied sulfate-reducing microorganism species; the bar in the upper right is 0.5 micrometre long.

Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate (SO2−
4) as terminal electron acceptor, reducing it to hydrogen sulfide (H2S).[1][2] Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration.

Most sulfate-reducing microorganisms can also reduce some other oxidized inorganic sulfur compounds, such as sulfite (SO2−
3), dithionite (S
2O2−
4), thiosulfate (S
2O2−
3), trithionate (S
3O2−
6), tetrathionate (S
4O2−
6), elemental sulfur (S8), and polysulfides (S2−
n). Other than sulfate reduction, some sulfate-reducing microorganisms are also capable of other reactions like disproportionation of sulfur compounds. Depending on the context, "sulfate-reducing microorganisms" can be used in a broader sense (including all species that can reduce any of these sulfur compounds) or in a narrower sense (including only species that reduce sulfate, and excluding strict thiosulfate and sulfur reducers, for example).

Sulfate-reducing microorganisms can be traced back to 3.5 billion years ago and are considered to be among the oldest forms of microbes, having contributed to the sulfur cycle soon after life emerged on Earth.[3]

Many organisms reduce small amounts of sulfates in order to synthesize sulfur-containing cell components; this is known as assimilatory sulfate reduction. By contrast, the sulfate-reducing microorganisms considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory sulfate reduction.[4] They use sulfate as the terminal electron acceptor of their electron transport chain.[5] Most of them are anaerobes; however, there are examples of sulfate-reducing microorganisms that are tolerant of oxygen, and some of them can even perform aerobic respiration.[6] No growth is observed when oxygen is used as the electron acceptor.[7] In addition, there are sulfate-reducing microorganisms that can also reduce other electron acceptors, such as fumarate, nitrate (NO−
3), nitrite (NO−
2), ferric iron (Fe3+), and dimethyl sulfoxide (DMSO).[1][8]

In terms of electron donor, this group contains both organotrophs and lithotrophs. The organotrophs oxidize organic compounds, such as carbohydrates, organic acids (such as formate, lactate, acetate, propionate, and butyrate), alcohols (methanol and ethanol), aliphatic hydrocarbons (including methane), and aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylene).[9] The lithotrophs oxidize molecular hydrogen (H2), for which they compete with methanogens and acetogens in anaerobic conditions.[9] Some sulfate-reducing microorganisms can directly use metallic iron (Fe0, also known as zerovalent iron, or ZVI) as an electron donor, oxidizing it to ferrous iron (Fe2+).[10]

  1. ^ a b Cite error: The named reference NR was invoked but never defined (see the help page).
  2. ^ Ernst-Detlef Schulze; Harold A. Mooney (1993), Biodiversity and ecosystem function, Springer-Verlag, pp. 88–90, ISBN 9783540581031
  3. ^ Cite error: The named reference BF was invoked but never defined (see the help page).
  4. ^ Rückert, Christian (2016). "Sulfate reduction in microorganisms—recent advances and biotechnological applications". Current Opinion in Microbiology. 33: 140–146. doi:10.1016/j.mib.2016.07.007. PMID 27461928.
  5. ^ Larry Barton, ed. (1995), Sulfate-reducing bacteria, Springer, ISBN 9780306448577
  6. ^ Kasper U. Kjeldsen; Catherine Joulian & Kjeld Ingvorsen (2004). "Oxygen Tolerance of Sulfate-Reducing Bacteria in Activated Sludge". Environmental Science and Technology. 38 (7): 2038–2043. Bibcode:2004EnST...38.2038K. doi:10.1021/es034777e. PMID 15112804.
  7. ^ "Simone Dannenberg; Michael Kroder; Dilling Waltraud & Heribert Cypionka (1992). "Oxidation of H2, organic compounds and inorganic sulfur compounds coupled to reduction of O2 or nitrate by sulfate-reducing bacteria". Archives of Microbiology. 158 (2): 93–99. doi:10.1007/BF00245211. S2CID 36923153.
  8. ^ Plugge, Caroline M.; Zhang, Weiwen; Scholten, Johannes C. M.; Stams, Alfons J. M. (2011). "Metabolic Flexibility of Sulfate-Reducing Bacteria". Frontiers in Microbiology. 2: 81. doi:10.3389/fmicb.2011.00081. ISSN 1664-302X. PMC 3119409. PMID 21734907.
  9. ^ a b Liamleam, Warounsak; Annachhatre, Ajit P. (2007). "Electron donors for biological sulfate reduction". Biotechnology Advances. 25 (5): 452–463. doi:10.1016/j.biotechadv.2007.05.002. PMID 17572039.
  10. ^ Kato, Souichiro (2016-03-01). "Microbial extracellular electron transfer and its relevance to iron corrosion". Microbial Biotechnology. 9 (2): 141–148. doi:10.1111/1751-7915.12340. ISSN 1751-7915. PMC 4767289. PMID 26863985.