No abstract

SummaryPyoverdines, the main siderophores of fluorescent pseudomonads, contain a peptide moiety, different for each pyoverdine, and an identical chromophore. While it has been shown that non-ribosomal peptide synthetases (NRPSs) are involved in the biosynthesis of the peptide chain of pyoverdines, this was not demonstrated for the biosynthesis of the chromophore part. We found that PvsA, from Pseudomonas fluorescens ATCC 17400, and PvdL (PA2424), from Pseudomonas aeruginosa are similar NRPSs and functional homologues, necessary for the production of pyoverdine. Transcriptional lac Z fusions showed that pvdL is co-transcribed with the upstream PA2425 gene, encoding a putative thioesterase, and is ironregulated via PvdS. Similarly, RT-PCR analysis revealed that expression of pvsA is repressed by iron. Analysis of the adenylation domains of PvsA, PvdL and their homologues, revealed that their N-terminus starts with an acyl-CoA ligase module, followed by three amino acid activation domains. Computer modelling of these domains suggests that PvsA in P. fluorescens and PvdL in P. aeruginosa are orthologues involved in the biosynthesis of the pyoverdine chromophore.

Characteristic fragment ions of the various chromophores of the pyoverdin siderophore family obtained by collision activated dissociation of the [M+2H]2+ ions are reported allowing unambiguous identification. Tandem mass spectrometrical studies revealed the existence of the first example of a ferribactin with a succinamide side chain, and they add some information to the problem in which way a malic acid side chain is attached to the chromophore.