Many members of the Pseudomonas genus are important phytopathogens (P. syringae), phytostimulators (P. fluorescens), or opportunistic pathogens of animals, plants, insects, and fungi (P. aeruginosa). Type IV pili-related functions that contribute to the colonization and infection process include mediating initial adhesion to host tissues, colony expansion via twitching motility, and the development of intractable biofilms that are recalcitrant to host immune attack and antibiotic therapy.
Type IV pili have been shown to mediate attachment of various P. syringae pathovars to the leaves of both susceptible and non-susceptible plants. P. syringae tfp mutants show significantly reduced adhesion to plant tissues and the ability to generate symptoms in host plants when spray inoculated also correlates with the presence of tfp.181,184-185 Taken together these results indicate that tfp-mediated adhesion of P. syringae phytopathogens to plant tissues is an important factor in the disease process. Tfp may also play a role in colonization of tomato roots by the plant growth promoting P. fluorescens WCS365.138 The identity of specific plant receptors, if any, for tfp-mediated adhesion to plant tissues has not been established.
P. aeruginosa is an important opportunistic pathogen of humans but is also a pathogen of plants, animals, and yeast. Various plant (Arabidopsis, lettuce, basil, and alfalfa), animal (mouse, rat, hamster, nematode, fruit fly, and moth) and yeast (Candida albicans) models of infection have been developed to identify and characterize virulence genes of P. aeruginosa. To date, the involvement of P. aeruginosa tfp in infection of plants or nematodes has not been investigated. As mentioned above, it has been shown that P. aeruginosa tfp are not required for virulence of Drosophila melanogaster (fruit fly).55 It has also been demonstrated that rpoN mutants of P. aeruginosa (which do not produce tfp), are not impaired in virulence of Galleria mellonella (greater wax moth).96 Thus it seems that tfp are not essential for virulence in these insect pathogenicity models. P. aeruginosa tfp are, however, involved in initial attachment to filamentous C. albicans103 and are essential for virulence in various mouse models of infection.40,47,75,88,217,249
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