Structure of pseudobactin 7SR1, a siderophore from a plant-deleterious Pseudomonas

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Abstract
When grown in Fe-limiting culture medium, sugar beet deleterious Pseudomonas 7SR1 produced extracellularly the yellow-green, fluorescent siderophore pseudobactin 7SR1. Pseudobactin 7SR1 had a molecular formula of C46H63N13O23 and a molecular mass of 1166 g/mol. Pseudobactin 7SR1 contained a cyclic octapeptide with the amino acid sequence L-Ala-Gly-Ser-Ser-threo-.beta.-OH-Asp-Thr-Ser-N.delta.-OH-Orn. Since pseudobactin 7SR1 was not affected by nonspecific enzymes, it might contain D-amino acids. A yellow-green, fluorescent quinoline derivative is postulated to be attached via an ester bond to the serine residue following the glycine. A malamide group was attached to C 3 of the quinoline derivative. The 3 bidentate Fe (III)-chelating groups consisted of an .alpha.-hydroxy acid group derived from .beta.-hydroxyaspartic acid, an o-dihydroxyl aromatic group derived from the yellow-green, fluorescent chromophore and a hydroxamate group derived from N.delta.-acetyl-N.delta.-hydroxyornithine. The chemical structure of pseudobactin 7SR1 is remarkably similar to that of pseudobactin, the siderophore of plant growth promoting Pseudomonas B10.