Synthesis of peptide-modified pyoverdins by a fluorescent Pseudomonas strain grown in isoleucine-supplemented medium

The pattern of pyoverdin-type siderophores produced by Pseudomonas putida BTP16 in iron-limited succinate medium supplemented or not with isoleucine was characterized by electrospray ionization mass spectrometry. Two new compounds were observed in culture supernatants from BTP16 grown in the presence of isoleucine. For both molecules, mass differences with pyoverdins originally synthesized by the strain were only interpreted considering the incorporation of Ile into the peptide chain. Further evidence supporting this phenomenon was provided by radioactivity incorporation in pyoverdins produced in the presence of C-14-labeled Ile. Our results are discussed in relation to the non-ribosomal mechanism supposed to be involved in the synthesis of these molecules.