Structures and characteristics of novel siderophores from plant deleterious Pseudomonas fluorescens A225 and Pseudomonas putida ATCC 39167

When Pseudomonas putida ATCC 39167 and plant-deleterious Pseudomonas fluorescens A225 were grown in an iron-deficient culture medium, they each produced two different novel yellow green fluorescent pseudobactins: P39167- I, II and PA225-I, II. Pseudobactin P39167-I has a molecular formula of C₄₆H₆₅O₂₃N₁₃ and is monoanionic at neutral pH. P39167-II has the molecular formula of C₄₆H₆₃O₂₂N₁₃ and no charge at neutral pH. Pseudobactin PA225-I has a molecular formula of C₄₆H₆₅O₂₄N₁₃ and is monoanionic at neutral pH whereas pseudobactin PA225-II has the molecular formula of C₄₆H₆₃O₂₃N₁₃ and no charge at neutral pH. All four of the pseudobactins contain a dihydroxyquinoline-based chromophore. The amino acid sequence for the octapeptide in case of pseudobactins from P. putida ATCC 39167 is Chr-Ser(1)-Ala(1)-AcOHOrn-Gly-Ala(2)-OHAsp-Ser(2)-Thr. In case of pseudobactins from P. fluorescens A225, the octapeptide has the sequence Chr- Ser(1)-Ala-AcOHOrn-Gly-Ser(2)-OHAsp-Ser(3)-Thr. For all four pseudobactins (P39167-I, II and PA225-I, II), the serine(1) residue of the octapeptide is attached to the carboxylic acid group on the C-11 of the fluorescent quinoline via an amide bond. Additionally, for pseudobactin P39167-II and PA225-II, the hydroxyl group of the serine(1) residue is also attached to the carboxyl group of threonine residue at the carboxy terminus of the peptide via an ester bond, resulting in a cyclic depsipeptide in contrast to the linear peptide chain of P39167-I and PA225-I. For all four pseudobactins, a malamide group is attached to the C-3 of the quinoline derived chromophore. The three bidentate iron(III) chelating groups in all four pseudobactins consist of a 1,2-dihydroxy aromatic group of the fluorescent chromophore, a hydroxy acid group of β-hydroxy aspartic acid, and a hydroxamate group from the acylated N(δ)-hydroxyornithine. The amino acid constituents of the pseudobactins P39167 I, II are the same as those in pseudobactin A214, whereas those in A225 I, II are the same as in 7SR1, but in both cases the sequences are different. The uptake results indicate a single outer membrane receptor protein for ferric-pseudobactins in both organisms. The receptor proteins in the two species are similar but not identical.