Résumé
The Vfm quorum sensing (QS) system is preponderant for the virulence of different species of the phytopathogenic bacteria of the genus Dickeya. In the model strain D. dadantii 3937, the Vfm QS system was shown to be responsible for the control of the production of plant cell wall degrading enzymes (PCWDEs). The transduction of the Vfm QS signal results into the activation of the promoter of the gene vfmE encoding a transcriptional regulator of the AraC family which itself activates the promoter of PCWDE genes. The vfm gene cluster includes 26 genes involved in the biosynthesis, sensing or transduction of the QS signal. It encodes several nonribosomal peptide synthetases (NRPS), indicating that the Vfm QS signal is a complex short peptide. To date, the Vfm QS signal has escaped detection by analytical chemistry methods. Using a strain-specific polymorphism in the NRPS genes vfmO and vfmP was shown to determine the production of different analogs of the Vfm QS signal. By analogy with the Agr QS system of Staphylococcus aureus, the production of different analogs of the signal is expected to be related to variations in the signal transduction activity of the Vfm QS system, resulting in variations in the level of activation of the promoter of the regulator gene vfmE. To explore this hypothesis, we used a reporter gene fused to the promoter of the gene vfmE to compare the activity of the vfmE promoter among strains of Dickeya producing different analogs of the Vfm QS signal.