Active Transport and Accumulation of Iodide by Newly Isolated Marine Bacteria

Abstract

Iodide (I؊ )-accumulating bacteria were isolated from marine sediment by an autoradiographic method with radioactive 125 I ؊ . When they were grown in a liquid medium containing 0.1 M iodide, 79 to 89% of the iodide was removed from the medium, and a corresponding amount of iodide was detected in the cells. Phylogenetic analysis based on 16S rRNA gene sequences indicated that iodide-accumulating bacteria were closely related to Flexibacter aggregans NBRC15975 and Arenibacter troitsensis, members of the family Flavobacteriaceae. When one of the strains, strain C-21, was cultured with 0.1 M iodide, the maximum iodide content and the maximum concentration factor for iodide were 220 ؎ 3.6 (mean ؎ standard deviation) pmol of iodide per mg of dry cells and 5.5 ؋ 10 3 , respectively. In the presence of much higher concentrations of iodide (1 M to 1 mM), increased iodide content but decreased concentration factor for iodide were observed. An iodide transport assay was carried out to monitor the uptake and accumulation of iodide in washed cell suspensions of iodide-accumulating bacteria. The uptake of iodide was observed only in the presence of glucose and showed substrate saturation kinetics, with an apparent affinity constant for transport and a maximum velocity of 0.073 M and 0.55 pmol min ؊1 mg of dry cells ؊1 , respectively. The other dominant species of iodine in terrestrial and marine environments, iodate (IO 3 ؊ ), was not transported.

Hydrogen Peroxide-Dependent Uptake of Iodine by Marine Flavobacteriaceae Bacterium Strain C-21

“…After washing, cells were resuspended in the same buffer to achieve optical density at 600 nm of 1.0 (equivalent to 0.5 mg (dry weight)] ml Ϫ1 ). The transport assay was carried out essentially as described previously (4). Briefly, the cell suspension was incubated aerobically with 0.1 M potassium iodide and 74 kBq ml Ϫ1 radioactive iodine tracer (Na 125 I; Amersham Bioscience).…”

“…When C-21 was cultured in a liquid medium containing 0.1 M iodide, the strain removed 80% of iodide from the medium within 24 h and accumulated iodine in the cells with a maximum concentration factor of 5.5 ϫ 10 3 (4). The initial uptake rates of iodine by washed cells of C-21 showed substrate saturation kinetics with an apparent affinity constant for transport of 0.073 M. Interestingly, the cells took up iodine only in the presence of glucose (4). In this study, iodine transport by a washed cell suspension of C-21 was assayed for further understanding of the mechanism of iodine uptake by C-21.…”

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

“…Finally, HIO is translocated freely across the cell membrane. Since the initial rate of uptake by C-21 showed substrate saturation kinetics 7) , HIO is probably transported via carrier-mediated facilitated diffusion. In the cells, HIO should be reduced to iodide again, or be associated with certain organic compounds, to avoid a release of iodine from the cells.…”

“…In 2005, an iodine-accumulating bacterium, designated strain C-21, was isolated from surface marine sediment 7) . This strain was phylogenetically closely related to a marine aerobic bacterium, Arenibacter troitsensis, a member of the family Flavobacteriaceae.…”

Biogeochemical Considerations Related To The Remediation Of I-129 Plumes

“…Bacteria can accumulate iodine, through either electrostatic adsorption on the cell surface or via electrophilic substitution of cellular organic molecules. Strains isolated from seawater and marine sediments can concentrate iodide by a factor of 6 × 10 3 , but efforts to identify iodine accumulating strains from soils or among anaerobic bacteria common in subsurface aquifers failed (Amachi et al, 2010;Amachi et al, 2005a). Iodide accumulation ability was tested among 136 bacterial strains isolated from sediments of an 129 I-contaminated, aerobic aquifer in F Area of the SRS and three strains were identified that accumulated low levels of iodide (0.2 to 2.0% of a 0.1 μM solution; 1 -2 orders of magnitude less than that of the marine strains that accumulate iodide) .…”