Résumé
Background: To date, the only known small molecule synthesized by non-ribosomal peptide synthesis (NRPS) in the genus Xanthomonas is the phytotoxin albicidin produced by Xanthomonas albilineans, the causal agent of sugarcane leaf scald disease. Recent analyses of available genomic sequences indicated that X. albilineans, as well as Xanthomonas oryzae and Xanthomonas translucens, possess a novel NRPS gene cluster called META-B whose architecture is strainspecific (each sequenced strain is predicted to synthesize a different peptide) and doesn´t resemble to any NRPS gene cluster described to date. Because the META-B NRPS gene cluster is specific to three phylogenetically distant species of Xanthomonas associated with monocotyledonous plants, we assume a putative involvement of the new family of small molecules produced by this gene cluster in plant-bacteria interactions. Objectives: We aimed at isolating and characterizing the small molecule encoded by the META-B NRPS gene cluster of X. albilineans in order to study its putative involvement in plant-bacteria interactions. Methods: We developed a META-B overproducing X. albilineans strain by over-expressing the AraC transcriptional regulator which is present within the META-B NRPS gene cluster. HPLC profiles obtained from cultures of wild type vs the AraC over-expressing strain were compared. Peaks with significantly increased amplitude in the HPLC profile from the AraC over-expressing strain were collected and their content analyzed by mass spectrometry. Conclusions: We identified a peptide with a nominal molecular mass > 2 kDa and with an amino acid sequence (MS/MS experiments) which excellently matches the one predicted by A-domain specificities of META-B NRPS genes. (Texte intégral)