Novel Proteins That Modulate Type IV Pilus Retraction Dynamics in
Pseudomonas aeruginosaJournal Articles
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abstract
ABSTRACTPseudomonas aeruginosa
uses type IV pili to colonize various materials and for surface-associated twitching motility. We previously identified five phylogenetically distinct alleles of
pilA
in
P. aeruginosa
, four of which occur in genetic cassettes with specific accessory genes (J. V. Kus, E. Tullis, D. G. Cvitkovitch, and L. L. Burrows, Microbiology 150:1315-1326, 2004). Each of the five pilin alleles, with and without its associated pilin accessory gene, was used to complement a group II PAO1
pilA
mutant. Expression of group I or IV
pilA
genes restored twitching motility to the same extent as the PAO1 group II pilin. In contrast, poor twitching resulted from complementation with group III or group V
pilA
genes but increased significantly when the cognate
tfpY
or
tfpZ
accessory genes were cointroduced. The enhanced motility was linked to an increase in recoverable surface pili and not to alterations in total pilin pools. Expression of the group III or V pilins in a PAO1
pilA-pilT
double mutant yielded large amounts of surface pili, regardless of the presence of the accessory genes. Therefore, poor piliation in the absence of the TfpY and TfpZ accessory proteins results from a net increase in PilT-mediated retraction. Similar phenotypes were observed for
tfpY
single and
tfpY-pilT
double knockout mutants of group III strain PA14. A PilA
V
-TfpY chimera produced few surface pili, showing that the accessory proteins are specific for their cognate pilin. The genetic linkage between specific pilin and accessory genes may be evolutionarily conserved because the accessory proteins increase pilus expression on the cell surface, thereby enhancing function.
