Figure 1: Quorum sensing in V. fischeri. Two AHL autoinducers (N-3-oxo-HSL synthesized by LuxI and C8-HSL synthesized by AinS) and AI-2 are present in V. fischeri utilized for bioluminescence regulation in a cell-population-dependent manner. At a high cell concentration, N-3-oxo- HSL impinges on the N-terminal of LuxR, unmasking the HTH domain and resulting in the expression of bioluminescence. The relative kinase/phosphatase activities of the hybrid sensor AinR and LuxQ towards LuxU are dependent on the concentrations of their respective AIs. Phosphorylation of LuxO triggers the transcription of the sRNA, Qrr1 which degrades the litR mRNA in the presence of Hfq. LitR takes part in luminescence regulation by direct activation of the expression of LuxR.