Structure of pseudobactin A214, a siderophore from a bean-deleterious Pseudomonas

Abstract

Bean-deleterious Pseudomonas A214 produced the extracellular yellow-green, fluorescent siderophore [microbial iron(III) transport agent] pseudobactin A214 under iron-limiting conditions. Pseudobactin A214 had a molecular formula of C46H64N13O22 and a molecular mass of 1151 g/mol. Pseudobactin A214 contained an N-blocked linear octapeptide with the amino acid sequence Ser-Ala-Gly-Ser-Ala-threo-.beta.-OH-Asp-L-allo-Thr-N.delta.-OH-Orn with a yellow-green, fluorescent quinoline derivative attached via an amide bond to the amino terminus. A succinamide group was linked to carbon 3 of the quinoline derivative. Sequencing was accomplished by two-dimensional NMR spectroscopy and by Edman degradation of smaller peptides obtained from partial acid hydrolysis. Since pseudobactin A214 was not affected by nonspecific proteolytic enzymes, it might contain D-amino acids. The three bidentate iron-(III)-chelating groups consisted of a 1,2-dihydroxy aromatic group in the quinoline chromophore, an .alpha.-hydroxy acid group present as .beta.-hydroxyaspartic acid, and a hydroxamate group derived from N.delta.-acetyl-N.delta.-hydroxyornithine. The chemical structure of pseudobactin A214 is remarkably similar to those of pseudobactin and pseudobactin 7SR1, the siderophores of plant growth promoting and plant-deleterious Pseudomonas B10 and Pseudomonas 7SR1, respectively.