A) The principle of QS-mediated swarming in P. aeruginosa. B) Simplified regulatory framework. The system has a single QS signal S (that in vivo corresponds to C12-3-oxo-AHL and C4-AHL). If the level of S exceeds a certain threshold level, the cell becomes activated. Production of S is increased by a positive feedback loop, and production of a factor F starts. F corresponds to all secreted factors (i.e. "public goods") such as surfactants, enzymes, siderophores, and so on, that the cells secrete into the environment. If the concentration of F exceeds a threshold, the cells start to swarm: they increase their movement, nutrient intake, and metabolism.