Mutasynthesis of siderophore analogues by Pseudomonas aeruginosa

The Gram-negative bacterium Pseudomonas aeruginosa produces the phenolic siderophore pyochelin. Salicylic acid is an intermediate in the pyochelin biosynthetic pathway, and mutants blocked in salicylic acid biosynthesis (Sal-) are able to incorporate exogenously supplied salicylic acid into pyochelin. A P. aeruginosa Sal- mutant was incubated with 13 salicylic acid analogues and was found to incorporate three (5-fluorosalicylic acid, 4-methylsalicylic acid, and 3-hydroxypicolinic acid) into pyochelin analogues, trivially designated as 5-fluoropyochelin, 4-methylpyochelin, and 6-azapyochelin. The structures of the mutasynthetic products were confirmed by 1H and 13C NMR and high-resolution fast atom bombardment mass spectrometry as being identical to pyochelin except for the expected changes in the aromatic ring. The biological activity of the three pyochelin analogues was determined in iron transport assays. In comparison to pyochelin, 4-methylpyochelin was more active in the assays whereas the activities of 5-fluoropyochelin and 6-azapyochelin were markedly decreased. In coincubation assays, 5-fluoropyochelin substantially inhibited iron transport by pyochelin; 4-methylpyochelin and 6-azapyochelin did not demonstrate this inhibitory effect.