Reduction of Hypoiodous Acid by Shewanella oneidensis MR-1 Using Extracellular Electron Transfer Components

Hypoiodous acid (HIO) represents a pivotal iodine species in global iodine cycling, yet microbial contributions to its transformation have remained poorly characterised. Here, we demonstrate that the metal-reducing bacterium Shewanella oneidensis MR-1 actively drive HIO reduction to iodide. Notably, genetic disruption of extracellular electron transfer components impaired HIO reduction activity in S. oneidensis MR-1. Specifically, ΔmtrCAB reduced 49.7% less HIO than the wild type within 10 min, while ΔdmsEFAB exhibited a slight impairment in HIO reduction. The mutants lacking outer-membrane c-type cytochromes (MtrC and OmcA) also showed substantially lower reduction efficiencies (29.6%-54.0%) than wild type. Although flavin secretion was not essential for HIO reduction in S. oneidensis MR-1, reduced riboflavin chemically reacted with HIO to generate iodide. Importantly, both the mtrC/omcA deletions and exogenous HIO addition inhibited iodate reduction, suggesting HIO reduction serves as a detoxification mechanism. In contrast, electron shuttles dose-dependently enhanced iodate reduction. Collectively, these results demonstrate that Shewanella-mediated HIO reduction constitutes a rapid detoxifying pathway for HIO, with the MtrCAB-OmcA transmembrane electron conduit acting as the primary mediator. However, the DmsEFAB pathway and endogenous electron shuttles showed limited contributions.