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

Iodate (IO 3 - ) 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 IO 3 - reaction and the relative contribution of abiotic and biotic IO 3 - 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 3 - by Fe(II) produced intermediates HIO and I - at a ratio of 1:2, followed by HIO disproportionation to I - and IO 3 - . Comparative analyses of IO 3 - 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 IO 3 - reduction by biogenic Fe(II) predominated under iron-rich conditions, while biotic IO 3 - 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 3 - in the presence of Fe(III) oxides and clay minerals. The observed abiotic and biotic IO 3 - 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.