DsrAB

DsrAB refers to the two-subunit dissimilatory sulfite reductase enzyme, a central component of the dissimilatory sulfate reduction pathway in many sulfate-reducing microorganisms. The enzyme is a heterodimer encoded by dsrA and dsrB genes, forming the DsrAB complex that catalyzes the reduction of sulfite to sulfide, a key step in energy metabolism for organisms that respire sulfate.

The DsrAB enzyme contains siroheme and multiple iron-sulfur clusters, housed in the A and B subunits. The A subunit typically carries the siroheme cofactor and a [4Fe-4S] center, while the B subunit contains additional Fe-S binding domains. Electrons are shuttled to DsrAB via membrane-associated complexes (such as DsrMKJOP) and other electron donors, driving the six-electron reduction of sulfite to sulfide within the cytoplasm. In sulfur-oxidizing bacteria, a reverse pathway that uses DsrAB for sulfide oxidation to sulfite has been described in certain lineages.

Genetically, dsrA and dsrB reside in the dsr operon, often alongside dsrC and other accessory genes (dsrD, dsrM, dsrK, dsrJ, dsrO, dsrN). DsrC, a small sulfurtransfer protein, participates in processing sulfur intermediates linked to DsrAB activity. DsrAB is widely distributed among sulfate-reducing prokaryotes (and some sulfur-oxidizing microbes), making it a common molecular marker for studying the microbial sulfate reduction and sulfur cycle.

Ecologically, DsrAB-dependent sulfate reduction is a major anaerobic process in marine and freshwater sediments and subsurface environments, influencing organic matter degradation and biogeochemical sulfur fluxes. The dsrAB genes are routinely targeted in environmental genomics to identify and quantify sulfate-reducing communities and to infer their ecological roles.