Global occurrence of the bacteria with capability for extracellular reduction of iodate

Abstract

The γ-proteobacterium Shewanella oneidensis MR-1 reduces iodate to iodide extracellularly. Both dmsEFAB and mtrCAB gene clusters are involved in extracellular reduction of iodate by S. oneidensis MR-1. DmsEFAB reduces iodate to hypoiodous acid and hydrogen peroxide (H2O2). Subsequently, H2O2 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 dmsEFAB and mtrCAB gene clusters. The dmsEFAB and mtrCAB gene clusters were found in three Ferrimonas and 26 Shewanella species. Coexistence of both dmsEFAB and mtrCAB 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 dmsEFAB and mtrCAB 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 dmsEFAB and mtrCAB gene clusters also varied substantially. The identified mtrCAB gene clusters often contained additional genes for multiheme c-type cytochromes. The numbers of dmsEFAB gene cluster detected in a given bacterial genome ranged from one to six. In latter, duplications of dmsEFAB gene clusters occurred. These results suggest different paths for these bacteria to acquire their capability for extracellular reduction of iodate.

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

“…IR-12, contributed to IO 3 − reduction in seawater. 13,18 Given the widespread distribution of Shewanella species and other bacteria containing the dmsEFAB and mtrCAB gene clusters in oceans, 17,19 the role of S. oneidensis MR-1 in abiotic and biotic IO 3 − reduction in this study suggests that the Fe(III)-reducing microorganism may also participate in IO 3 − reduction in ocean. IO 3 − reduction and subsequent I − oxidation with O 3 in surface seawater releases gaseous iodine to the atmosphere and thus impacts air quality and climate.…”

“…Coexistence of both dmsEFAB and mtrCAB gene clusters in the genome is a prerequisite for driving both enzymatical IO 3 – reduction and abiotic IO 3 – reduction by biogenic Fe­(II). Our previous genome analysis indicated that the bacteria with the dmsEFAB and mtrCAB gene clusters were widely distributed in lakes, rivers, and subsurface and marine environments, which suggests their importance in global biogeochemical cycling through abiotic and biotic IO 3 – reduction …”

“…Our previous genome analysis indicated that the bacteria with the dmsEFAB and mtrCAB gene clusters were widely distributed in lakes, rivers, and subsurface and marine environments, which suggests their importance in global biogeochemical cycling through abiotic and biotic IO 3 − reduction. 19…”

“…The intermediate HIO is disproportionated into I – and IO 3 – . The widespread distribution of bacteria harboring both dmsEFAB and mtrCAB gene clusters suggests their importance in the global biogeochemical cycling of iodine . In addition to facilitating microbial IO 3 – reduction, MtrCAB reduces different forms of Fe­(III), such as Fe­(III)-citrate, Fe­(III) oxides, and Fe­(III)-containing clay minerals .…”

Review on the physical chemistry of iodine transformations in the oceans

“…Recently, Shin et al (2022) showed that Shewanella oneidensis requires extracellular dimethylsulfoxide (DMSO) reductase involving a molybdenum enzyme center for IO − 3 reduction. Guo et al (2022) studied bacterial genomes in a variety of environments and documented that Shewanella oneidensis are ubiquitous in all fresh and marine waters; they concluded that IO − 3 reduction is a major biogeochemical process. Thus, nitrate reductase (also an O atom transfer reaction) is not a requirement for bacterial IO − 3 reduction to I -.…”