The γ-proteobacterium MR-1 reduces iodate to iodide extracellularly. Both and gene clusters are involved in extracellular reduction of iodate by MR-1. DmsEFAB reduces iodate to hypoiodous acid and hydrogen peroxide (HO). Subsequently, HO is reduced by MtrCAB to facilitate DmsEFAB-mediated extracellular reduction of iodate. To investigate the distribution of bacteria with the capability for extracellular reduction of iodate, bacterial genomes were systematically searched for both and gene clusters. The and gene clusters were found in three and 26 species. Coexistence of both and gene clusters in these bacteria suggests their potentials for extracellular reduction of iodate. Further analyses demonstrated that these bacteria were isolated from a variety of ecosystems, including the lakes, rivers, and subsurface rocks in East and Southeast Asia, North Africa, and North America. Importantly, most of the bacteria with both and gene clusters were found in different marine environments, which ranged from the Arctic Ocean to Antarctic coastal marine environments as well as from the Atlantic Ocean to the Indian and Pacific Oceans. Widespread distribution of the bacteria with capability for extracellular reduction of iodate around the world suggests their significant importance in global biogeochemical cycling of iodine. The genetic organization of and gene clusters also varied substantially. The identified gene clusters often contained additional genes for multiheme -type cytochromes. The numbers of gene cluster detected in a given bacterial genome ranged from one to six. In latter, duplications of gene clusters occurred. These results suggest different paths for these bacteria to acquire their capability for extracellular reduction of iodate.