Dissimilatory Iodate Reduction by Marine Pseudomonas sp. Strain SCT

Abstract

Bacterial iodate (IO 3؊ ) reduction is poorly understood largely due to the limited number of available isolates as well as the paucity of information about key enzymes involved in the reaction. In this study, an iodatereducing bacterium, designated strain SCT, was newly isolated from marine sediment slurry. SCT is phylogenetically closely related to the denitrifying bacterium Pseudomonas stutzeri and reduced 200 M iodate to iodide (I ؊ ) within 12 h in an anaerobic culture containing 10 mM nitrate. The strain did not reduce iodate under the aerobic conditions. An anaerobic washed cell suspension of SCT reduced iodate when the cells were pregrown anaerobically with 10 mM nitrate and 200 M iodate. However, cells pregrown without iodate did not reduce it. The cells in the former category showed methyl viologen-dependent iodate reductase activity (0.31 U mg ؊1 ), which was located predominantly in the periplasmic space. Furthermore, SCT was capable of anaerobic growth with 3 mM iodate as the sole electron acceptor, and the cells showed enhanced activity with respect to iodate reductase (2.46 U mg ؊1 ). These results suggest that SCT is a dissimilatory iodate-reducing bacterium and that its iodate reductase is induced by iodate under anaerobic growth conditions.

Microbial Contribution to Global Iodine Cycling: Volatilization, Accumulation, Reduction, Oxidation, and Sorption of Iodine

“…Malate, lactate, glycerol, glucose, succinate and acetate could serve as the electron donor. These results suggest that SCT is a dissimilatory iodatereducing bacterium, and that its periplasmic iodate reductase is induced by iodate under anaerobic growth conditions 5) . Considering the high redox potential of iodate reduction Fig.…”

“…Although both types of cells showed similar levels of nitrate reductase activity, only the former cells (pregrown with iodate) showed methyl viologen-dependent iodate reductase activity, which was located predominantly in the periplasmic space. Furthermore, SCT was capable of anaerobic growth with 2 to 4 mM iodate as the sole electron acceptor 5) . The growth was nearly proportional to the iodate concentration in the medium.…”

“…Recently, an iodate-reducing bacterium, designated strain SCT, was newly isolated from marine sediment 5) . Strain SCT was phylogenetically closely related to a denitrifying bacterium, Pseudomonas stutzeri, and reduced 200 μM iodate to iodide within 12 h in an anaerobic culture containing 10 mM nitrate.…”

Transformation of iodate to iodide in marine phytoplankton driven by cell senescence

“…2b & 3b). The increase in bacteria goes hand in hand with the increase in iodide, and we cannot totally rule out that bacteria also reduce a certain amount of iodate to iodide as they are capable of doing so (Tsunogai & Sase 1969, Amachi et al 2007. In all other cultures, bacteria were minor constituents and can be neglected (Figs.…”

Iodide Oxidation by a Novel Multicopper Oxidase from the Alphaproteobacterium Strain Q-1

“…Iodine is present in seawater at a concentration of 0.45 M (50), and the predominant chemical forms are iodide (I Ϫ ; oxidation state, Ϫ1), iodate (IO 3 Ϫ ; oxidation state, ϩ5), and organic iodine compounds (14,35,44,50,53). In the biogeochemical cycling of iodine, microorganisms may play important roles, together with marine algae and phytoplankton, through the production (1,2) and remineralization (27,28) of organic iodine compounds and the redox changing of inorganic iodine species, i.e., iodide and iodate (3,4). Oxidation of iodide is an important process in the redox cycling of iodine, but little is known about the mechanism of this reaction in nature.…”