The Pseudomonas aeruginosa Type IV pilus-associated protein PilY1 is required for stable fiber formation and host attachment

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that is a leading cause of hospital-acquired pneumonia and the primary pathogen associated with chronic respiratory infection in individuals with cystic fibrosis (CF). P. aeruginosa pathogenesis involves a wide variety of virulence factors; including secreted toxins, Type II and type III secretion systems, quorum sensing, biofilms, flagellum, and Type IV pili (TFP). TFP are long surface fibers composed primarily of pilin subunits, and are known to function in both a specialized form of movement known as twitching motility and attachment to host cells and tissues. An exposed epitope on the terminal pilin subunit of TFP is believed to mediate P. aeruginosa binding to host glycosphingolipids. We hypothesized that PilY1, a putative minor pilus-associated protein, may play a direct role in TFP-dependent bacterial adherence due to its homology to a known TFP-associated adhesin in Neisseria gonorrhoeae, PilC. We confirmed a previous report that pilY1 is required for pilus biogenesis, though this requirement is dependant on the presence of PilT. We demonstrated PilY1 is required for adherence to injured Human Airway Epithelial (HAE) cells, indicating a potential role as a TFP-associated adhesin. This adherence requires the association of PilY1 with surface TFP fibers, a process that involves a set of pilin-like proteins (FimU, PilV, PilW, PilX, and PilE). Overall, our results indicate that adherence of P. aeruginosa to host cell requires both TFP and PilY1 and that PilY1 is a bi-functional protein with distinct roles in TFP biogenesis and adherence