Hierarchical organization of the CepIR, CciIR and CepR2 quorum sensing systems and traits under their control in B. cenocepacia K56-2. Summary diagram of the regulatory interrelationship between CepIR and CciIR, and CciIR and CepR2. AHLs are required to activate CepR and CciR but not CepR2. All three regulators negatively control their own expression. The three QS systems positively and negatively influence gene expression. +, positive regulation; -, negative regulation.