Isolation and Characterization of an Fe(III)-Chelating Compound Produced by Pseudomonas syringae

The phytopathogenic bacterium Pseudomonas syringae produces a fluorescent pigment when it is grown in iron-deficient media. This pigment forms a very stable Fe(III) complex that was purified in this form by using a novel procedure based on ultrafiltration and column chromatography. The Fe(III) complex has a molecular weight of 1,100 and contains 1 mol of Fe(III). The pigment is composed of an amino acid moiety with three threonines, three serines, one lysine, delta-N-hydroxyornithine, and a quinoline-type fluorescent chromophore. These features and its stability constant (in the range of 10) suggest that the fluorescent pigment of P. syringae is related to the siderophores produced by another Pseudomonas species.