Multiple roles of Pseudomonas aeruginosa TBCF10839 PilY1 in motility, transport and infection

Abstract

SummaryPolymorphonuclear neutrophils are the most important mammalian host defence cells against infections with Pseudomonas aeruginosa. Screening of a signature tagged mutagenesis library of the non-piliated P. aeruginosa strain TBCF10839 uncovered that transposon inactivation of its pilY1 gene rendered the bacterium more resistant against killing by neutrophils than the wild type and any other of the more than 3000 tested mutants. Inactivation of pilY1 led to the loss of twitching motility in twitching-proficient wild-type PA14 and PAO1 strains, predisposed to autolysis and impaired the secretion of quinolones and pyocyanin, but on the other hand promoted growth in stationary phase and bacterial survival in murine airway infection models. The PilY1 population consisted of a major full-length and a minor shorter PilY1* isoform. PilY1* was detectable in small extracellular quinolone-positive aggregates, but not in the pilus. P. aeruginosa PilY1 is not an adhesin on the pilus tip, but assists in pilus biogenesis, twitching motility, secretion of secondary metabolites and in the control of cell density in the bacterial population.

Minor Pilins of the Type IV Pilus System Participate in the Negative Regulation of Swarming Motility

“…While this is a broad brushstroke in terms of compartmentalizing these proteins, such observations allow for the possibility of interaction among these proteins. However, previous reports have found PilY1 present in sheared surface protein fractions, indicating that PilY1 is a cell surface-localized protein, possibly associated with the pilus (7,21). Thus, we cannot rule out the possibility that signaling by PilY1 occurs through a more complex mechanism involving communication between the outer cell surface and inner membrane compartment.…”

Pseudomonas aeruginosa Minor Pilins Prime Type IVa Pilus Assembly and Promote Surface Display of the PilY1 Adhesin

“…We propose that calcium binding by PilY1 causes a conformational change, similar to opening of a drywall anchor, that enhances adhesiveness and/or prevents re-entry into the cell upon retraction. As a result, a minor pilin-PilY1 complex may be retracted only as far as the outside of the secretin but not re-enter the cell, explaining why PilY1 has been reported to be both T4aP-and cell surface-associated (21,22). This scenario could allow for efficient pilus re-extension, because major subunits need only be added at the base of an existing pilus stub.…”

“…The proposed functions of the minor pilins include priming of assembly, counteracting retraction, contributing to adhesion, and/or modulating the balance between pilus extension and retraction (15,(17)(18)(19)(20). The P. aeruginosa minor pilins FimU and PilVWXE are encoded in a polycistronic operon with PilY1, a large (ϳ125 kDa) non-pilin protein implicated in anti-retraction, attachment, and other T4P-related functions (17,(21)(22)(23)(24) (Fig. 1).…”

Type IV Pilin Proteins: Versatile Molecular Modules

“…Although AlgR controls other operons as well, provision of the minor pilin genes in trans is sufficient to restore twitching motility. Inactivation of individual genes in the minor pilin operon of P. aeruginosa resulted in increased expression of others, implying a positive-feedback loop in the absence of specific components (53,154). In Neisseria, the genes encoding the core minor pilins PilHIJK are clustered with the gene for the noncore minor pilin, PilX (called PilL in some N. gonorrhoeae strains [416]), while the loci encoding other noncore proteins (PilV and ComP) are unlinked.…”

“…N. meningitidis isolates use PilC1 and PilC2 to adhere to the uropods of neutrophils in order to escape phagocytosis (362). P. aeruginosa expresses an integrinbinding PilC homolog, called PilY1, that requires the T4P system for surface localization, although its direct association with pili has not yet been demonstrated convincingly (13,53,174,204). Mutation of PilY1 homologs in plant pathogens has also been associated with defects in motility and biofilm formation (252,310).…”