The roles of DmsEFAB and MtrCAB in extracellular reduction of iodate by Shewanella oneidensis   MR ‐1 with lactate as the sole electron donor

To investigate their roles in extracellular reduction of iodate (IO₃ ⁻ ) with lactate as an electron donor, the gene clusters of dmsEFAB, mtrCAB, mtrDEF and so4360-4357 in Shewanella oneidensis MR-1 were systematically deleted. Deletions of dmsEFAB and/or mtrCAB gene clusters diminished the bacterial ability to reduce IO₃ ⁻ . Furthermore, DmsEFAB and MtrCAB worked collaboratively to reduce IO₃ ⁻ of which DmsEFAB played a more dominant role than MtrCAB. MtrCAB was involved in detoxifying the reaction intermediate hydrogen peroxide (H₂ O₂ ). The reaction intermediate hypoiodous acid (HIO) was also found to inhibit microbial IO₃ ⁻ reduction. SO4360-4357 and MtrDEF, however, were not involved in IO₃ ⁻ reduction. Collectively, these results suggest a novel mechanism of extracellular reduction of IO₃ ⁻ at molecular level, in which DmsEFAB reduces IO₃ ⁻ to HIO and H₂ O₂ . The latter is further reduced to H₂ O by MtrCAB to facilitate the DmsEFAB-mediated IO₃ ⁻ reduction. The extracellular electron transfer pathway of S. oneidensis MR-1 is believed to mediate electron transfer from bacterial cytoplasmic membrane, across the cell envelope to the DmsEFAB and MtrCAB on the bacterial outer membrane.