to surface associated behaviors

The opportunistic pathogen Pseudomonas aeruginosa explores surfaces using twitching motility powered by type IV pili (TFP). Single cells also use TFP to sense the surface, and respond by upregulating many genes associated with virulence. To twitch and sense surfaces, cells cyclically extend, attach and retract their TFP. Both TFP activity and mechanosensing depend on activation of a chemotaxis-like system called Chp. However, how TFP activates the Chp system and how this feeds back on TFP activity remains unknown. Here we show that Chp activation by TFP provides a positive feedback on its activity. We first demonstrate that surface contact increases twitching motility in a Chp-dependent manner. Using localization of fluorescent protein fusions and measurements of piliation by interferometric scattering microscopy, we highlight the mechanism by which the chemotaxis like system controls motility, independently of transcriptional feedback.