Abiotic and Biotic Reduction of Iodate Driven by MR-1.

Iodate (IO) can be abiotically reduced by Fe(II) or biotically reduced by the dissimilatory Fe(III)-reducing bacterium (MR-1) via its DmsEFAB and MtrCAB. However, the intermediates and stoichiometry between the Fe(II) and IO reaction and the relative contribution of abiotic and biotic IO reduction by biogenic Fe(II) and MR-1 in the presence of Fe(III) remain unclear. In this study, we found that abiotic reduction of IO by Fe(II) produced intermediates HIO and I at a ratio of 1:2, followed by HIO disproportionation to I and IO. Comparative analyses of IO reduction by MR-1 wild type (WT), MR-1 mutants deficient in DmsEFAB or MtrCAB, and sp. ANA-3 in the presence of Fe(III)-citrate, Fe(III) oxides, or clay minerals showed that abiotic IO reduction by biogenic Fe(II) predominated under iron-rich conditions, while biotic IO reduction by DmsEFAB played a more dominant role under iron-poor conditions. Compared to that in the presence of Fe(III)-citrate, MR-1 WT reduced more IO in the presence of Fe(III) oxides and clay minerals. The observed abiotic and biotic IO reduction by MR-1 under Fe-rich and Fe-limited conditions suggests that Fe(III)-reducing bacteria could contribute to the transformation of iodine species and I enrichment in natural iodine-rich environments.