Significance of MccR, MccC, MccD, MccL and 8-methylmenaquinone in sulfite respiration of Wolinella succinogenes

Reduction of sulfite to sulfide is an essential step in the biogeochemical sulfur cycle. The Epsilonproteobacterium Wolinella succinogenes uses the copper-containing octahaem cytochrome c sulfite reductase MccA to respire sulfite. MccA is encoded by the first gene of the mcc gene cluster, whose transcription is apparently induced by the two-component regulatory system MccRS. It has been proposed that the iron‑sulfur protein MccC, the putative quinol dehydrogenase MccD, the copper chaperone MccL as well as menaquinone-6 (MK6) and/or 8-methylmenaquinone-6 (8-MMK6) are involved in the electron transport chain of W. succinogenes sulfite respiration. Here, non-polar W. succinogenes mutants were constructed that lacked MccC, MccD, MccL or the 8-MMK6-producing MK6 methyltransferase MqnK. Each mutant possessed a frameshift-corrected mccR gene, thus inducing mcc expression in the presence of a mixture of fumarate and sulfite as terminal electron acceptors. Under these conditions, growth by sulfite respiration of cells lacking MccA, MccC or MccD was found to be abolished. However, cells lacking MccL or 8-MMK6 still coupled formate oxidation to sulfite reduction and grew by sulfite respiration to some extent. The results indicate that MccR, MccC, MccD, MccL and 8-MMK6 are essential or significant components of W. succinogenes sulfite respiration. [Display omitted] •The two-component system MccRS regulates production of the respiratory Mcc system.•The electron transfer proteins MccC and MccD are essential for sulfite respiration.•The putative copper chaperone MccL and methylmenaquinone are significant.