FIG. 1.

Quorum sensing in P. aeruginosa. In P. aeruginosa, secreted components such as proteases (LasB elastase), rhamnolipids, and pyocyanin are under the transcriptional control of two quorum-sensing systems, las and rhl. Both systems involve a transcriptional regulator (LasR and RhlR, respectively) and an autoinducer synthase (LasI and RhlI, respectively). When the bacterial density reaches a threshold, the accumulation in the medium of signaling autoinducer molecules (• and ▪) induces the las and rhl pathways, leading to transcription of virulence genes. The las quorum-sensing system can also induce, to some extent, the rhl quorum-sensing system. SOD, superoxide dismutase.