How Pseudomonas aeruginosa Regulates Surface Behaviors

T he opportunistic pathogen Pseudomonas aeruginosa displays several behaviors when it encounters solid or semisold surfaces. For instance, the bacterial cells form biofilms, swarm, and engage in pili-mediated twitching. Although each of these group behaviors is extensively studied on its own, little is known about the relationships among these behaviors. As P. aeruginosa cells transition from planktonic growth in liquids to life on solid surfaces, each cell first interacts with the substratum. Subsequent to contacting that surface, cells might display any of these three surface-only behaviors, leading one to suspect that P. aeruginosa coregulates these behaviors. Here we focus on one specific regulatory feature of group surface behaviors, namely the inverse control of biofilm formation and swarming motility. For the sake of this article, biofilms are defined as surface-associated communities of microbes that produce an extracellular matrix, which consists in part of extracellular polysaccharides. When such cells engage in swarming motility, they depend on flagella and surfactants to move across surfaces.