Dissimilatory sulfate reduction

Overview of dissimilatory sulfate reduction performed by sulfate-reducing microorganisms.

Dissimilatory sulfate reduction is a form of anaerobic respiration that uses sulfate as the terminal electron acceptor. This metabolism is found in some types of bacteria and archaea which are often termed sulfate-reducing organisms.

Dissimilatory sulfate reduction occurs in three steps:

  1. Conversion (activation) of sulfate to Adenosine 5’-phosphosulfate (APS)
  2. reduction of APS to sulfite
  3. reduction of sulfite to sulfide

Which requires the consumption of a single ATP molecule and the input of 8 electrons (e−).[1][2]

The protein complexes responsible for these chemical conversions — Sat, Apr and Dsr — are found in all currently known organisms that perform dissimilatory sulfate reduction.[3] Energetically, sulfate is a poor electron acceptor for microorganisms as the sulfate-sulfite redox couple is E0' -516 mV, which is too negative to allow reduction by NADH or ferrodoxin that are the primary intracellular electron mediators.[4] To overcome this issue, sulfate is first converted into APS by the enzyme ATP sulfurylase (Sat), at the cost of a single ATP molecule. The APS-sulfite redox couple has a E0' of -60 mV, which allows APS to be reduced by either NADH or reduced ferrodoxin using the enzyme adenylyl-sulfate reductase (Apr), which requires the input of 2 electrons.[4] In the final step, sulfite is reduced by the dissimilatory sulfite reductase (Dsr) to form sulfide, requiring the input of 6 electrons.[2]

Note. The term "dissimilatory" is used when hydrogen sulfide is produced in an anaerobic respiration process. By contrast, the term "assimilatory" would be used in relation to the biosynthesis of organo-sulfur compounds.

References

  1. ↑ Barton, Larry L.; Fardeau, Marie-Laure; Fauque, Guy D. (2014). "Chapter 10. Hydrogen Sulfide: A Toxic Gas Produced by Dissimilatory Sulfate and Sulfur Reduction and Consumed by Microbial Oxidation". In Peter M.H. Kroneck and Martha E. Sosa Torres. The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment. Metal Ions in Life Sciences. 14. Springer. pp. 237–277. doi:10.1007/978-94-017-9269-1_10.
  2. 1 2 Grein F, Ramos AR, Venceslau SS, Pereira IA (February 2013). "Unifying concepts in anaerobic respiration: insights from dissimilatory sulfur metabolism". Biochim. Biophys. Acta. 1827 (2): 145–60. doi:10.1016/j.bbabio.2012.09.001. PMID 22982583.
  3. ↑ Pereira IA, Ramos AR, Grein F, Marques MC, da Silva SM, Venceslau SS (2011). "A comparative genomic analysis of energy metabolism in sulfate reducing bacteria and archaea". Front Microbiol. 2: 69. doi:10.3389/fmicb.2011.00069. PMC 3119410Freely accessible. PMID 21747791.
  4. 1 2 Muyzer G, Stams AJ (June 2008). "The ecology and biotechnology of sulphate-reducing bacteria". Nat. Rev. Microbiol. 6 (6): 441–54. doi:10.1038/nrmicro1892. PMID 18461075.
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