sulfatereduction

Sulfate reduction is a form of anaerobic respiration in which sulfate (SO4^2−) serves as the terminal electron acceptor and is reduced to hydrogen sulfide (H2S). It is carried out by sulfate-reducing bacteria and archaea (SRB and SRA) that inhabit anoxic environments such as marine and freshwater sediments, wetlands, rice paddies, and oil reservoirs. The process plays a major role in the global sulfur cycle, coupling sulfur and carbon metabolism and influencing metal mobility through sulfide production.

The term includes two related but distinct pathways: dissimilatory sulfate reduction, in which sulfate is used for energy generation and the resultant sulfide is excreted, and assimilatory sulfate reduction, in which sulfate is reduced for biosynthesis (for example, cysteine) and does not contribute to energy yield.

For dissimilatory sulfate reduction, the pathway begins with activation of sulfate to adenosine-5'-phosphosulfate (APS) by ATP sulfurylase. APS is reduced to sulfite by APS reductase (AprAB), and sulfite is further reduced to sulfide by dissimilatory sulfite reductase (DsrAB) with associated electron transfer cofactors. The process utilizes electron donors such as hydrogen, lactate, acetate, or other organic compounds, and couples oxidation of these substrates to sulfate reduction.

Ecological and practical aspects: SRB contribute to mineral cycling and metal sulfide formation; their activity can lead to souring of oil reservoirs and corrosion of metal infrastructure due to biogenic hydrogen sulfide. They also have potential in bioremediation and in the treatment of sulfide-containing waste streams under anaerobic conditions.