Iodate reduction by marine aerobic bacteria.

Iodate reductase (Idr) gene cluster ( ) is involved in bacterial iodate (IO ) respiration under anaerobic conditions. Putative gene clusters are present in both anaerobic and aerobic bacteria; however, the specific physiological roles of genes in aerobic bacteria remain unclear. Therefore, in this study, three marine aerobic bacteria with putative gene clusters (, , and ) were grown in the presence of iodate to determine whether they can reduce iodate to iodide (I). All tested bacteria almost completely reduced 2 mM iodate under static conditions but only reduced 0.1-0.5 mM iodate under shaking conditions. Moreover, the washed cell suspension of reduced iodate only when the cells were pre-grown statically in the presence of iodate. Transcriptional analysis revealed that the expression levels of , , , and genes were upregulated in when the cells were grown statically in the presence of iodate. Specifically, expression was induced by 0.1 μM iodate and was up to 14-fold higher compared to that of the non-iodate control. These results suggest that marine aerobic bacteria reduce iodate under oxygen-limited conditions, and that this capacity is induced by environmentally relevant levels of iodate in seawater. Our results suggest that marine aerobic bacteria contribute to iodide production in marine surface waters, thereby affecting the global iodine cycling and ozone budget.