Interference in quorum sensing and virulence of the phytopathogen Pseudomonas syringae pv. passiflorae by Bacillus and Variovorax species

Abstract

Pathogenic bacteria often engage in a form of cell-to-cell communication termed quorum sensing (QS) to coordinate the expression of multiple virulence factors. Therefore, interference of QS has potential as a means of controlling bacterial-mediated plant diseases. Accordingly, this study was aimed at: (1) identifying QS signals produced by the phytopathogen, Pseudomonas syringae pv. passiflorae, and (2) evaluating interference in QS and virulence of the pathogen by putative N-acyl homoserine lactone (AHL)-degrading Bacillus and Variovorax species as a biocontrol strategy. Detection of AHLs using the biosensor strain and high-resolution mass spectroscopy suggested that P. syringae pv. passiflorae produced N-tetradecanoyl homoserine lactone and N-hexanoyl homoserine lactone as quorum-sensing signal molecules. Evaluation of putative AHL-degrading bacteria as biocontrol agents, through a series of inhibition assays (inhibition of motility, biofilm and virulence factors), suggested that bacteria which targets AHLs could be used to control P. syringae pv. passiflorae. We further demonstrated that putative AHL-degrading Bacillus and Variovorax species prevented hypersensitivity in tomato plants by P. syringae pv. passiflorae. Taken together, these results indicated that putative AHL-degrading bacteria were potential biocontrol agents against P. syringae pv. passiflorae and reinforced the idea that disrupting QS and associated virulence factors could be an effective method in controlling plant pathogens.