Azotobacter vinelandii grown in iron-limited medium containing 1 mu M
molybdate released the catecholate siderophores azotochelin and aminoc
helin [bis(2,3-dihydroxybenzoyl-lysine) and 2,3-dihydroxybenzoyl-putre
scine, respectively] into the culture fluid, However these catecholate
s 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 th
e culture fluid in the presence of high molybdate, Full and partial ac
id 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 protoch
elin was iron-repressible and protochelin very rapidly decolorized the
Chrome Azurol-S assay. Protochelin promoted the growth of the siderop
hore-deficient A. vinelandii strain P100 under iron-restricted conditi
ons and promoted Fe-55 uptake into iron-limited cells, confirming that
protochelin can be used as a siderophore by A. vinelandii.