Production of the triacetecholate siderophore protochelin by Azotobacter vinelandii

Azotobacter vinelandii grown in iron-limited medium containing 1 m molybdate released the catecholate siderophores azotochelin and aminochelin bis(2,3-dihydroxybenzoyl-lysine) and 2,3-dihydroxybenzoyl-putrescine, respectively] into the culture fluid. However these catecholates were not observed when the medium contained 1 mm molybdate, but were replaced by another catecholate compound. The appearance of this new compound was not an artifact of extraction of the catecholates from the culture fluid in the presence of high molybdate. Full and partial acid hydrolysis and fast atom bombardment mass spectroscopy showed that the new compound was the tricatecholate protochelin, a product of the condensation of azotochelin and aminochelin. The production of protochelin was iron-repressible and protochelin very rapidly decolorized the Chrome Azurol-S assay. Protochelin promoted the growth of the siderophore-deficient A. vinelandii strain P100 under iron-restricted conditions and promoted ⁵⁵Fe uptake into iron-limited cells, confirming that protochelin can be used as a siderophore by A. vinelandii.