dsrABgenen

dsrAB genes encode the catalytic subunits of dissimilatory sulfite reductase, an enzyme central to microbial sulfur metabolism. The genes, dsrA and dsrB, are typically found together in an operon (dsrAB) in many sulfate-reducing bacteria and in some sulfur-oxidizing bacteria that operate the reverse pathway. Because their presence strongly correlates with the ability to reduce sulfite, dsrAB is widely used as a molecular marker for organisms that participate in dissimilatory sulfate reduction and related sulfur transformations.

At the protein level, DsrA and DsrB form a heterodimer that contains a siroheme cofactor and iron-sulfur clusters essential for electron transfer during catalysis. In organisms performing sulfite reduction, electrons derived from the cell’s metabolism are passed through membrane-associated complexes to DsrAB, driving the reduction of sulfite to sulfide. In some sulfur-oxidizing bacteria, the same enzyme operates in reverse, contributing to sulfide oxidation to sulfite as part of a reverse dissimilatory pathway.

dsrAB genes are widely distributed across bacteria and archaea, with distinct phylogenetic lineages separating many sulfate reducers from sulfide-oxidizing lineages. The genes are part of larger dsr operons that often include dsrC and dsrD, and in many systems connect to membrane complexes such as DsrMKJOP that shuttle electrons in and out of DsrAB. Lateral gene transfer events have shaped the current distribution of dsrAB sequences.

Due to their ecological role in the sulfur cycle, dsrAB genes are frequently targeted in environmental genomics and metagenomics to assess sulfate-reducing potential in soils, sediments, and anaerobic digesters. They also inform studies of bioremediation, oil-field souring, and the evolution of anaerobic respiration.