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

Abstract To investigate their roles in extracellular reduction of iodate (IO 3 − ) 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 IO 3 − . Furthermore, DmsEFAB and MtrCAB worked collaboratively to reduce IO 3 − of which DmsEFAB played a more dominant role than MtrCAB. MtrCAB was involved in detoxifying the reaction intermediate hydrogen peroxide (H 2 O 2 ). The reaction intermediate hypoiodous acid (HIO) was also found to inhibit microbial IO 3 − reduction. SO4360‐4357 and MtrDEF, however, were not involved in IO 3 − reduction. Collectively, these results suggest a novel mechanism of extracellular reduction of IO 3 − at molecular level, in which DmsEFAB reduces IO 3 − to HIO and H 2 O 2 . The latter is further reduced to H 2 O by MtrCAB to facilitate the DmsEFAB‐mediated IO 3 − 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.