FIG. 5.

Working model for the role of QS in P. aeruginosa PUPa3. Both QS systems positively regulate swimming, swarming (with the Rhl system being more important than the Las system), lipase, root colonization, and antifungal activity; the LasI/R system positively regulates protease activity, while RhlI/R does not regulate this activity. The two systems acting independently of each other and are not hierarchically organized. The LasI/R system produces 3-oxo-C12-HSL and undergoes positive autoregulation. The RhlI/R system produces C4-HSL and C6-HSL (C4 is the cognate AHL), and it also undergoes positive autoregulation. Both systems together are necessary for the infection of C. elegans and G. mellonella, whereas both independently are important for rhizosphere colonization. RsaL is a negative regulator of the LasI/R system and it is important for nematocidal killing, for antifungal activity, and for root colonization.