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