Abiotic and Biotic Reduction of Iodate Driven by <i>Shewanella oneidensis</i> MR‑1

Iodate (IO3–) can be abiotically reduced by Fe­(II) or biotically reduced by the dissimilatory Fe­(III)-reducing bacterium Shewanella oneidensis (MR-1) via its DmsEFAB and MtrCAB. However, the intermediates and stoichiometry between the Fe­(II) and IO3– reaction and the relative contribution of abiotic and biotic IO3– 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 IO3– by Fe­(II) produced intermediates HIO and I– at a ratio of 1:2, followed by HIO disproportionation to I– and IO3–. Comparative analyses of IO3– reduction by MR-1 wild type (WT), MR-1 mutants deficient in DmsEFAB or MtrCAB, and Shewanella sp. ANA-3 in the presence of Fe­(III)-citrate, Fe­(III) oxides, or clay minerals showed that abiotic IO3– reduction by biogenic Fe­(II) predominated under iron-rich conditions, while biotic IO3– 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 IO3– in the presence of Fe­(III) oxides and clay minerals. The observed abiotic and biotic IO3– 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