Uptake of iodide in the marine haptophyte Isochrysis sp. (T.ISO) driven by iodide oxidation

Abstract

Uptake of iodide was studied in the marine microalga Isochrysis sp. (isol. Haines, T.ISO) during short-term incubations with radioactive iodide ((125) I(-) ). Typical inhibitors of the sodium/iodide symporter (NIS) did not inhibit iodide uptake, suggesting that iodide is not taken up through this transport protein, as is the case in most vertebrate animals. Oxidation of iodide was found to be an essential step for its uptake by T.ISO and it seemed likely that hypoiodous acid (HOI) was the form of iodine taken up. Uptake of iodide was inhibited by the addition of thiourea and of other reducing agents, like L-ascorbic acid, L-glutathione and L-cysteine and increased after the addition of oxidized forms of the transition metals Fe and Mn. The simultaneous addition of both hydrogen peroxide (H2 O2 ) and a known iodide-oxidizing myeloperoxidase (MPO) significantly increased iodine uptake, but the addition of H2 O2 or MPO separately, had no effect on uptake. This confirms the observation that iodide is oxidized prior to uptake, but it puts into doubt the involvement of H2 O2 excretion and membrane-bound or extracellular haloperoxidase activity of T.ISO. The increase of iodide uptake by T.ISO upon Fe(III) addition suggests the nonenzymatic oxidation of iodide by Fe(III) in a redox reaction and subsequent influx of HOI. This is the first report on the mechanism of iodide uptake in a marine microalga.

Characterization of Iodine-Related Molecular Processes in the Marine Microalga Tisochrysis lutea (Haptophyta)

“…However, the dependence of perox expression on environmental iodide (and not iodate), as revealed by threshold mRNA abundance and the response to H 2 O 2 , indicates that this gene could be a putative haloperoxidase. A previous study of our group indicated that iodide uptake in T. lutea could possibly be promoted by an enzymatic oxidation using H 2 O 2 (van Bergeijk et al, 2013). The similarity of perox with peroxidase-cyclooxygenases in metazoans and its origin by HGT, as previously discussed, makes this gene a good candidate to participate in iodide metabolism processes such as uptake and organification and it could thus also have an impact on the biosynthesis of TH-like-compounds.…”

“…In addition to its nutritional value, T. lutea is a microalga that accumulates thyroid hormone (TH)-like compounds (Heyland and Moroz, 2005), indicating a particular iodide-related metabolism, what confers novel functional characteristics. Previous data of our group demonstrated this microalga is able to incorporate iodide from the environment after oxidation by enzymatic (haloperoxidase-mediated) or non-enzymatic ways (catalyzed by iron) (van Bergeijk et al, 2013(van Bergeijk et al, , 2016. Moreover, a fraction of intracellular iodine is organified as TH-like hormones (Heyland and Moroz, 2005).…”

Conceptual Model of Iodine Behavior in the Subsurface at the Hanford Site

“…Accumulation of iodine in other algal species and diatoms has also been demonstrated (Manley 2009, Osterc and Stibilj 2012, Shimura et al 2012, Thorenz et al 2014, van Bergeijk et al 2013). Regardless of the species, uptake appears to occur through the mechanism of a haloperoxidase, with or without hydrogen peroxide.…”

Senescence as the main driver of iodide release from a diverse range of marine phytoplankton

“…There is currently hardly any knowledge if and how this process takes place in natural seawater. Estimates of the lifetime of iodide due to oxidation in natural seawater range between less than 6 months and 40 years (Campos et al, 1996;Edwards and Truesdale, 1997;Tsunogai, 1971). Reported abiotic rates are too slow to explain the shorter lifetimes, so biogenic iodide oxidation driven by phytoplankton (Bluhm et al, 2010) or bacteria (Amachi, 2008;Fuse et al, 2003;Zic et al, 2013) has been suggested, but there remains great uncertainty surrounding this process (Truesdale, 2007).…”