Iron Transport in Microalgae: the Isolation and Biological Activity of a Hydroxamate Siderophore from the Blue-Green Alga Agmenellum quadruplicatum

Abstract

Supernatants from iron-deficient cultures of the marine, coccoid blue-green alga Agmenellum quadruplicatum strain PR-6 contained a chloroform-soluble iron-binding hydroxamate which was stimulatory for the growth of Arthrobacter jlavescens JG-9. Production of this material was maximal at 1 μM-Fe, was temperature dependent, and was increased by adding NH4 +. At the absorption maximum of 430 nm the At of the purified ferric complex was 32. The iron-free compound yielded nitroso dimers on periodate oxidation and was 60% as active on a weight basis for growth of Arth. flavescens as ferrioxamine B. At concentrations as low as 1 ng ml−l the purified hydroxamate stimulated growth of iron-depleted Agm. quadruplicatum in a chemically defined medium. Growth factor activity for Arth. flavescens JG-9 was also found in the supernatants and/or cell extracts of other blue-green algae and several diatoms grown under low-iron conditions.