Nonreductive Iron Uptake Mechanism in the Marine Alveolate Chromera velia    

Abstract

Chromera velia is a newly cultured photosynthetic marine alveolate. This microalga has a high iron requirement for respiration and photosynthesis, although its natural environment contains less than 1 nM of this metal. We found that this organism uses a novel mechanism of iron uptake, differing from the classic reductive and siderophore-mediated iron uptake systems characterized in the model yeast Saccharomyces cerevisiae and present in most yeasts and terrestrial plants. C. velia has no transplasma membrane electron transfer system, and thus cannot reduce extracellular ferric chelates. It is also unable to use hydroxamate siderophores as iron sources. Iron uptake from ferric citrate by C. velia is not inhibited by a ferrous chelator, but the rate of uptake is strongly decreased by increasing the ferric ligand (citrate) concentration. The cell wall contains a large number of iron binding sites, allowing the cells to concentrate iron in the vicinity of the transport sites. We describe a model of iron uptake in which aqueous ferric ions are first concentrated in the cell wall before being taken up by the cells without prior reduction. We discuss our results in relation to the strategies used by the phytoplankton to take up iron in the oceans.

A Comparative Study of Iron Uptake Mechanisms in Marine Microalgae: Iron Binding at the Cell Surface Is a Critical Step

“…It is likely that there is an iron-binding step at the cell surface prior to uptake, as suggested previously (Hudson and Morel, 1990;Sutak et al, 2010). This binding step differed between algae species and varied according to the cell iron status.…”

Surface binding, localization and storage of iron in the giant kelp Macrocystis pyrifera

“…8,9 Recent examples of possible surface concentration of iron come from the diatoms, the Alveolate Chromera velia, and Ectocarpus siliculosus where in some cases there is evidence that the surface bound iron is ultimately internalized. [10][11][12] While efficient transport mechanisms for iron uptake are an essential element in all pro-and eukaryotic cells, its intracellular availability and storage has to be tightly regulated, not only to buffer supply and demand, but also to prevent cell damage from undesirable reactions of free radicals, formed catalytically by free Fe ions. Ferritin represents the most common form of iron storage in all domains of life.…”

Uptake of iron by Kluyveromyces marxianus DSM 5422 cultivated in a whey‐based medium

“…(14). Here, the iron-uptake rate was determined under growth conditions in a real cultivation process but not in an artificial environment, as usual (e. g. iron absorption measured in short-term tests using resting cells [32,[35][36][37][38]50]).…”

“…The iron-uptake rates for S. cerevisiae, for the most part measured in short-term experiments under nongrowth conditions, were given related to the cell numbers but not the biomass (e.g. [32,[36][37][38]).…”