Elucidation of the functional role of flagella in virulence and ecological traits of Pseudomonas cichorii using flagella absence (δfliJ) and deficiency (δfliI) mutants

Understanding the infection mechanisms of pathogens will lead to better management of the associated diseases. The flagella of these pathogens play significant roles not only in bacterial motility, but also in virulence. In the present study, two genes involved in flagella construction, fliJ and fliI of Pseudomonas cichorii, were analyzed. The results revealed that these genes are vital for flagella formation and play significant roles not only in motility, but also in virulence. When we inoculated host plants with fliI- and fliJ-defective mutants (δfliJ and δfliI) through the dipping method, the degree of disease severity caused by both mutants was significantly reduced compared to those of the wild-type. However, the virulence of δfliI was stronger than that of δfliJ. Electron microscope observation, and swarming and leaf attachment assays indicated a reduced number of flagella in δfliI, but not complete absence, because of the presence of another copy of fliI. Furthermore, a vacuum infiltration assay revealed that flagella are indispensable in the pre- and post-penetration stages for complete virulence. Overall, we created semi-defective (δfliI) and completely defective (δfliJ) mutants and elucidated the fact that flagella play significant roles in virulence of the pathogen at different stages of the infection process.