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.