ISOLATION AND PURIFICATION OF SIDEROPHORES PRODUCED BY CYANOBACTERIA, SYNECHOCOCCUS SP PCC-7942 AND ANABAENA-VARIABILIS ATCC-29413

New siderophores were isolated and purified from the spent growth medium of the cyanobacteria Synechococcus sp. PCC 7942 (Anacystis nidulans R2) and Anabaena variabilis ATCC 29413 by solvent extraction and thin-layer chromatography. For each species the siderophore was released into the medium when the cells were grown at low iron concentrations and was not found in the medium of cells grown in iron-sufficient medium. Through a series of biological and chemical tests, combined with spectral analysis, the dihydroxamate nature of each siderophore was confirmed. The siderophores produced by Synechococcus sp. PCC 7942 and A. variabilis had distinct relative molecular masses of 310-313 Da and 520-525 Da, respectively. Neither of the two strains produced Arnow-positive extracellular organics, which indicate the excretion of extracellular catechol-type siderophores.