Respiratory membrane complexes of Desulfovibrio

Despite many years of research the process of sulfate respiration is still not fully understood. The mechanisms and components associated with energy conservation have not been clearly identified, and the electron donors to the cytoplasmic adenosine 5'-phosphosulfate (APS) and sulfite reductases are not known. Recently, considerable progress has been achieved through genome analysis and other biochemical and genetic studies. This review presents our current knowledge of transmembrane redox complexes of Desulfovibrio spp. that are proposed to play a role in the respiratory electron transfer chain. Two of these complexes, Qmo and Dsr, are apparently conserved in all sulfate reducers, pointing to an essential role in sulfate respiration, most likely as electron donors to the APS and sulfite reductases, respectively. In contrast, the Hmc, 9Hc and Tmc complexes are only present in Desulfovibrio organisms, suggesting a role in alternative pathways. The presence of the latter complexes correlates with the large pool of periplasmic cytochromes c found in Desulfovibrio spp., which act as electron donors to the complexes upon periplasmic oxidation of hydrogen or formate. Future studies are required to establish the exact function of all the complexes discussed, namely, their electron donors and acceptors and their involvement in energy-conserving mechanisms.