Pseudomonas aeruginosa twitching motility: type IV pili in action.

Type IV pili (T4P) are one of the most common forms of bacterial and archaeal surface structures, involved in adherence, motility, competence for DNA uptake, and pathogenesis. Pseudomonas aeruginosa has emerged as one of the key model systems for the investigation of T4P structure and function. Although its reputation as a serious nosocomial and opportunistic pathogen is well deserved, its facile growth requirements and the ready availability of molecular tools have allowed for rapid advances in our understanding of how T4P are assembled; their contributions to motility, biofilm formation and virulence; and their complex regulation. This review covers recent findings concerning the three different types of T4P found in P. aeruginosa (type IVa, type IVb, and Tad) and provides details about the modes of translocation mediated by T4aP, the architecture and function of the T4aP assembly system, and the complex regulation of T4aP biogenesis and function.