PILI OF PSEUDOMONAS-SYRINGAE PATHOVAR SYRINGAE ENHANCE INITIATION OF BACTERIAL EPIPHYTIC COLONIZATION OF BEAN

Pseudomonas syringae pathovar syringae R32 expresses phage-phi 6-speci fic pill that function as adhesins anchoring bacterial cells to the su rface of plants. Phage-resistant piliated and non-piliated mutants wer e compared to the wild-type strain with regards to pellicle formation and performance during different phases of epiphytic colonization of b ush bean. The degree of piliation did not affect the ability of the st rains to grow on the undisturbed plant surface. The presence of pili d id, however, correlate strongly with the efficiency of the strains to initiate colonization from a liquid inoculation suspension if unadsorb ed bacteria were removed by rinsing. During early colonization, wild-t ype bacteria became virtually resistant to displacement by rinsing wit hin 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 fun ctional on the plant surface, explaining in part the difference in res istance to removal by rinsing.