Dissimilatory iodate-reducing microorganisms inhabit marine oxygen minimum zones

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ABSTRACT Based on theoretical thermodynamic calculations, microbial IO3− reduction precedes NO3− reduction, and it was previously proposed that dissimilatory iodate-reducing microorganisms (DIRMs) inhabit a unique niche above marine oxygen minimum zones (OMZs). Here we demonstrate that dissimilatory IO3− reduction lags behind NO3− reduction in two representative strains Azonexus hydrophilus NCP973 and Denitromonas iodatirespirans IR-12. Correspondingly, the functional genes idrABP1P2 for DIRMs were found to be exclusively distributed across depth profiles of global OMZs where NO3− reduction is active. Combined with widespread detection and heterologous expression of the idrABP1P2 of metagenome-assembled genomes (MAGs) from the OMZs, these findings suggest that DIRMs inhabit marine OMZs and contribute to I− production and accumulation. As OMZs expand under global warming, DIRMs could enhance volatile iodine fluxes to the atmosphere by producing the precursor I−. Given the environmental health importance of atmospheric iodine, integrating this pathway into marine iodine biogeochemical models will improve our capability of understanding and predicting the future changes in oceanic iodine emissions.

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