ALGAE AND CYANOBACTERIA RELEASE ORGANIC CHELATORS IN THE PRESENCE OF INORGANIC Fe(III) THUS KEEPING IRON DISSOLVED

The cells of the green unicellular alga Scenedesmus incrassatulus Böhl, strain R-83 released organic chelators for Fe(III) in inorganic nutrient medium both in iron-deficient and in iron-replete conditions. Iron-deficient cells released chelators capable to bind 11nmol Fe. mg (cell DW)–1.h–1, while the chelators released from iron-sufficient cells after contact with Fe(III) were sufficient to bind 1nmol Fe. (mg cell DW)–1.s–1. A perfect correlation existed between the capacity of humic complexes of Fe(III) to catalyze lipid peroxidation in lipid-containing extracts in vitro, and their capacity to trigger the release of organic chelators from cells in vivo. Chelator release was stimulated by oxygen and was blocked by DCMU in the dark. Inorganic Fe(II) induced fivefold lower chelator release than inorganic Fe(III). Fe(III)-induced release of chelators was also registered in seven algal strains (Chlorella, Scenedesmus, Porphyridium) and in two cyanobacterial strains: Arthronema (Plectonema) and Arthrospira (Spirulina).