PURIFICATION, CHARACTERIZATION, AND STRUCTURE OF PSEUDOBACTIN-589-A, A SIDEROPHORE FROM A PLANT-GROWTH PROMOTING PSEUDOMONAS

Under conditions of low-iron stress the plant growth promoting bacterium Pseudomonas putida 589 (DSM 50202) produced a yellow-green fluorescent iron-binding peptide siderophore, which was designated pseudobactin 589 A and had an affinity constant toward Fe3+ of 1025 at pH 7. Protonated pseudobactin 589 A had the molecular formula C54H78O26N15 and a nominal mass spectral molecular mass of 1353 g/mol. Its structure was determined by a combination of nuclear magnetic resonance, fast atom bombardment mass spectrometry, and Edman degradation. Pseudobactin 589 A consisted of a nonapeptide with the amino acid sequence L-Asp-L-Lys-(D)-β-OH-Asp-D(L)-Ser-L-Thr-D-Ala-D-Glu-L(D)-Ser-L-Nδ-OH-Orn, in which lysine was amide bonded via the carboxy and the Nє-amino groups. A quinoline-derived chromophore was connectd via an amide bond to the α-amino nitrogen of aspartic acid and an L-malamide residue was attached to the chromophore. The three bidentate Fe3+ binding ligands consisted of an o-dihydroxy aromatic group from the quinoline derivative, β-hydroxyaspartic acid, and an internally cyclized Nδ-hydroxyornithine. The structure of pseudobactin 589 A is unique but strikingly similar to that of other pseudobactin-type siderophores from other plant growth promoting and plant deleterious pseudomonads. © 1990, American Chemical Society. All rights reserved.