PilJ localizes to cell poles and is required for Type IV pilus assembly and extension in Pseudomonas aeruginosa

Twitching motility allows Pseudomonas aeruginosa to move along surfaces by extending and retracting its Type IV pili. PilJ is a protein necessary for this surface associated twitching motility and bears high sequence identity with Escherichia coli methyl-accepting chemotaxis proteins (MCP). Here we report that pill is required for twitching motility in common laboratory strains, as well as clinical and environmental isolates of P. aeruginosa. We show that wild type cells extend pili at a single pole, but pilJ mutants assemble shortened pili at both poles despite normal levels of pilin accumulation. Many Type IV pilus assembly proteins localize to the cell poles. We used a functional PilJ-YFP fusion protein to determine that PilJ is localized to both poles of the cell regardless of growth conditions. This localization is independent of many other polar proteins required for twitching motility, including PilT, PilU, PilB. Neither does its localization require certain proteins involved in the putative pil chemosensory system, PilI or PilH. Our data suggest a model in which PilJ facilitates switching the active pole for pilus assembly, extension and retraction which allows cells to switch direction without physically turning the cell.