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Suppression of bacterial soft-rot diseases utilizing plant phenolic compounds

Iris Yedidia: Agricultural Research Organization, The Volcani Center

<div><em>Pectobacteria</em> rely on N-acylhomoserine lactone (AHL) signaling to coordinate cell to cell communication and synchronize virulence in a collective behavior termed quorum sensing (QS). Plants in response produce an array of small molecules, several of which have been suggested as QS inhibitors, yet with no resolved mode of action at the atomic scale. Here, QS mutant analysis identified AHL synthase (ExpI), as a preferred target for QS inhibitors. Salicylic acid (SA), the plant defense signal, and the essential oil carvacrol (CAR), were demonstrated to inhibit the accumulation of AHL molecules at concentrations that did not affect bacterial growth or membrane integrity. The phenolics also impaired biofilm formation, exoenzyme activities and reduced bacterial virulence during infection of potato and calla lily.</p> <p>Docking simulations suggest that the phytochemicals interfere with QS by binding of SA/CAR to ExpI. The hypothesis was confirmed by Isothermal Titration Calorimetry and Microscale thermophoresis that demonstrated direct binding between the phenolics and purified ExpI. Furthermore, computational Ala scan served to design an ExpI mutant with a predicted weaker affinity to both ligands. Indeed, the computational predictions were confirmed with lower affinity values of SA and CAR to the mutant protein. The direct binding between phytochemicals and bacterial AHL synthase, reinforce interkingdom signaling between plant molecules and bacterial communication systems.</div>

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