Membrane vesicles traffic signals and facilitate group activities in a prokaryote

Many bacteria use extracellular signals to communicate and coordinate social activities, a process referred to as quorum sensing(1). Many quorum signals have significant hydrophobic character, and how these signals are trafficked between bacteria within a population is not understood. Here we show that the opportunistic human pathogen Pseudomonas aeruginosa packages the signalling molecule 2-heptyl-3-hydroxy-4-quinolone ( pseudomonas quinolone signal; PQS)(2) into membrane vesicles that serve to traffic this molecule within a population. Removal of these vesicles from the bacterial population halts cell - cell communication and inhibits PQS-controlled group behaviour. We also show that PQS actively mediates its own packaging and the packaging of other antimicrobial quinolines produced by P. aeruginosa into vesicles. These findings illustrate that a prokaryote possesses a signal trafficking system with features common to those used by higher organisms and outlines a novel mechanism for delivery of a signal critical for coordinating group behaviour in P. aeruginosa.