Figure 1. Schematic representation of QteE- and RsaL-dependent regulation of the P. aeruginosa las QS system.

In the pre-quorum period, QteE binds to the LasR receptor and prevents the binding of the LasR-3OC₁₂-HSL complex to the rsaL-lasI bidirectional promoter [20], hence delaying the onset of the QS response. Once the quorum has been reached, the LasR/3OC₁₂-HSL complex triggers the transcription of both rsaL and lasI genes. The consequent increase of 3OC₁₂-HSL levels, and thus of activated LasR, generates a positive feedback loop also responsible for the increase of RsaL levels. RsaL binding to the rsaL-lasI bidirectional promoter represses the expression of both rsaL and lasI genes, thus counteracting the positive feedback loop. This circuit provides 3OC₁₂-HSL homeostasis [24]. Solid arrows represent positive control; T-shaped lines represent negative control; dashed arrows indicate information flow; curved arrows represent the transcription start points of the indicated genes.