Pili of Pseudomonas syringae pathovar syringae enhance initiation of bacterial epiphytic colonization of bean

Abstract

SUMMARY: Pseudomonas syringae pathovar syringae R32 expresses phage-|6-specific pili that function as adhesins anchoring bacterial cells to the surface of plants. Phage-resistant piliated and non-piliated mutants were compared to the wild-type strain with regards to pellicle formation and performance during different phases of epiphytic colonization of bush bean. The degree of piliation did not affect the ability of the strains to grow on the undisturbed plant surface. The presence of pili did, however, correlate strongly with the efficiency of the strains to initiate colonization from a liquid inoculation suspension if unadsorbed bacteria were removed by rinsing. During early colonization, wild-type bacteria became virtually resistant to displacement by rinsing within 1 d after inoculation, whereas non-piliated mutant bacteria became only partly resistant within 3 d. Piliated cells formed a pellicle on the surface of stationary liquid cultures whereas non-piliated mutant strains did not. A mechanism similar to pellicle formation may be functional on the plant surface, explaining in part the difference in resistance to removal by rinsing.