HIGH-AFFINITY SIDEROPHORE-MEDIATED IRON-TRANSPORT SYSTEM IN THE GREEN-ALGA SCENEDESMUS-INCRASSATULUS

Under iron-deficient conditions a high-affinity siderophore-mediated i ron-transport system is induced in the green alga Scenedesmus incrassa tulus R-83. Algal siderophores have a strong avidity for ferric versus ferrous iron, quickly oxidate Fe(II) and efficiently solubilize Fe(II I) hydroxides. The entire ferrated molecule is translocated across the membrane by the specific transport system. The iron-uptake rate in Fe -deficient cells is higher at higher pH adjusted with bicarbonate in t he medium, suggesting the presence of an inducible membrane-bound ''tr anslocator''. The iron-reduction step is not involved in uptake of fer rated siderophores. The total absorbed iron from siderophores is high and does not strongly depend on the nutritional status of cells, showi ng that the critical step for iron uptake is siderophore secretion rat her than the membrane-bound iron-transport system.