Characterization of the diffusible signaling factor of Xylella fastidiosa CoDiRO strain.

Recent studies demonstrated that the virulence of Xylella fastidiosa relies on a fine balance
between more motile bacterial forms, able to move and proliferate within xylem vessels, and
sticky cells forming a biofilm, which are responsible for vessels blockage and insect
acquisition. This different behavior is regulated in a cell density-dependent manner by
diffusible signaling factors (DSFs), produced by the rpfF gene that initiates a transduction
cascade resulting in up- or down-regulation of several genes. Mainly DSFs identified in Xf
subspecies fastidiosa and having biological activity, consist of 2-cis unsaturated fatty acids
and particularly a 2-tetradecenoic (XfDSF1) and a 2-hexadecanoic acid (XfDSF2). The
characterization of these molecules has a direct application in a “pathogen confusion”
strategy for reducing the impact of Xf-infections since the approach consists in tricking the
pathogen, by altering DSF level in planta and lowering its virulence.
DSFs produced by the CoDiRO strain of Xf were extracted from bacterial culture media with
equal volumes of ethyl acetate (EtOAc). The EtOAc fractions, after drying over Na 2SO4, were
analyzed by Gas Chromatography-Mass Spectrometry analysis. Preliminary results showed
that a family of unsaturated fatty acids with a chain length of 12-18 carbon atoms is
produced. Their further full characterization and principal localization of the unsaturated
bond is in progress by 1 H nuclear magnetic resonance (NMR) and 13C NMR spectra.