Pectobacterium atrosepticum SCRI1043 flagella mediate adherence to potato plants indirectly through motility

Flagella are widely distributed appendages in bacteria with well-characterized functions in motility and chemotaxis. They also interact directly with hosts and, due to their ubiquity, are potent immune elicitors for hosts from both the plant and animal kingdoms. Furthermore, flagella have been shown to facilitate attachment for several different bacterial species, including several plant-associated bacteria to plant hosts. We previously demonstrated binding of flagella from Escherichia coli to ionic lipids in plant plasma membranes for horticultural species and Arabidopsis thaliana. As such, flagella could be considered as a generic colonization factor, especially in the early stages of the interactions. Therefore, we tested whether flagella from a genetically related species of plant pathogen, Pectobacterium atrosepticum, mediated binding to its susceptible plant host, potato, in a similar manner to E. coli. Surprisingly, flagella containing the filament flagellin from P. atrosepticum did not confer any binding advantage to potato roots. Furthermore, there was no direct interaction between purified flagella and potato membrane lipids (charged or uncharged). The binding capacity of Pectobacterium to potato is dependent upon the motility function of flagella, as both flagella-deficient and motor-deficient mutants were reduced in their binding to potato roots.