Direct observation of extension and retraction of type IV pili

Abstract

Type IV pili are thin filaments that extend from the poles of a diverse group of bacteria, enabling them to move at speeds of a few tenths of a micrometer per second. They are required for twitching motility, e.g., in Pseudomonas aeruginosa and Neisseria gonorrhoeae, and for social gliding motility in Myxococcus xanthus. Here we report direct observation of extension and retraction of type IV pili in P. aeruginosa. Cells without flagellar filaments were labeled with an amino-specific Cy3 fluorescent dye and were visualized on a quartz slide by total internal reflection microscopy. When pili were attached to a cell and their distal ends were free, they extended or retracted at rates of about 0.5 m s ؊1 (29°C). They also flexed by Brownian motion, exhibiting a persistence length of about 5 m. Frequently, the distal tip of a filament adsorbed to the substratum and the filament was pulled taut. From the absence of lateral deflections of such filaments, we estimate tensions of at least 10 pN. Occasionally, cell bodies came free and were pulled forward by pilus retraction. Thus, type IV pili are linear actuators that extend, attach at their distal tips, exert substantial force, and retract.Pseudomonas aeruginosa ͉ twitching motility ͉ fluorescence M otile bacteria swim, swarm, or glide. Gliding refers to movement on a solid surface, such as glass or hard agar, without flagella, usually in the direction of the long axis of a cell (1). One form of gliding, known either as twitching motility or as social gliding, depends on 6-nm diameter filaments called type IV pili that extend from the pole of a cell (2-6). Twitching cells can exhibit chemotaxis (7) and͞or phototaxis (8). Twitching motility is required for formation of biofilms (9), and social gliding is important for formation of fruiting bodies (10).We studied twitching motility in Pseudomonas aeruginosa, a common Gram-negative bacterium that acts as an opportunistic human pathogen. It causes bacteremia in burn victims, infections of the urinary tract in catheterized patients, chronic lung infections in patients with cystic fibrosis, and acute ulcerative keratitis in users of extended-wear soft-contact lenses (11,12). P. aeruginosa has a single flagellum and multiple type IV pili; thus, it can move by swimming or twitching motility. Pili-mediated adhesion is a known virulence factor (13) and the molecular genetics of pilus assembly has been studied extensively (14). It is thought that twitching motility allows cells to spread on body surfaces during infection (6).Type IV pili have been seen with an electron microscope (15, 16) but have not been visualized in vivo. Recently, the motion of bacterial flagella was analyzed by labeling intact cells with amino-specific fluorescent dyes (17). By labeling cells of P. aeruginosa with an amino-specific Cy3, we have observed directly pilus extension, pilus retraction, and retraction-mediated cell movement. Our work confirms and extends that of Mertz et al. (18), who used an optical trap to measure the force of retraction of pi...

Type IV pili mechanochemically regulate virulence factors in Pseudomonas aeruginosa

“…When assembled, TFP undergo thermal fluctuations in the vicinity of the substrate (22). Attachment of a TFP tip depends upon encountering the agarose surface.…”

Polarity of motility systems in Myxococcus xanthus

“…S-motility is similar to twitching motility in Pseudomonas aeruginosa [5], and is powered by retraction of the polar pili: pili are extruded from one cell pole, adhere to a surface or to another cell, and are then stimulated to retract [3]. Retraction of pili, triggered by specific attachment to polysaccharides or EPS, pulls cells in the direction of the sites of adhesion [3].…”

Pili de type IV

“…En effet, les pili de type IV ont ceci de particulier qu'ils sont dynamiques [3]. Ces longs (jusqu'à 30 microns soit plus de 10 fois la taille de la bactérie) polymères d'une même protéine (la pilin) peuvent être excrétés à des vitesses étonnantes (quelques microns par seconde) et permettent ainsi à la bactérie de sonder son environnement [4].…”