Illustration of the proposed model of the QS system in
LFI1238. The autoinducer synthases LuxS, LuxI and AinS, produce the different AHLs and AI-2 which are transported across the inner membrane (IM) and the outer membrane (OM). Their respective receivers are believed to be LuxPQ, a LuxR1-LuxR2 heterodimer, and AinR. The LuxS/LuxPQ pathway may be inactive due to a frame shift mutation within luxP. It is unknown which AHLs bind the LuxRs (illustrated with a question mark). At low cell density, a phosphorylation cascade is believed to start from the receivers LuxPQ and AinR, and proceed downstream to LuxO via LuxU (illustrated with dashed arrows). LuxO probably regulates expression of Qrr, which in turn controls the expression of the master regulator LitR. When the autoinducer concentrations are high, LitR is expressed and regulates the production of the AinS AHL, as well as activities such as motility, biofilm, adhesion, virulence and bioluminescence . Both LitR and the LuxRs are probably involved in regulation of the lux operon as illustrated.