Intercellular Signaling in Vibrio harveyi

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The long term goal of this research is to explore the molecular mechanisms that bacteria use for inter-cellular communication. This proposal focuses on a study of quorum sensing in the model bioluminescent marine bacterium Vibrio harveyi. V. harveyi has two quorum sensing circuits (Signalling System 1 and Signaling System 2) that converge to regulate light production (Lux). Each system is made up of a two-component sensor-autoinducer pair; LuxN/AI-1 for System 1 and LuxQ/AI-2 for System 2. Both sensors transduce information to a shared phosphorelay protein called LuxU, which in turn conveys the signal to the response regulator protein LuxO. Phospho-LuxO is indirectly responsible for repression of luciferase production at low cell density, because it activates the expression of a negative regulator of Lux. A transcriptional activator protein called LuxR is also required for expression of the luciferase structural operon. Results suggest that V. harveyi uses Signaling System 1 and AI-1 for intra-species communication and Signaling System 2 and AI-2 for inter-species communication. LuxO and RpoN are required for the repression of the expression of luminescence at low cell density. The hypothesis that both of these proteins are required for the activation of a repressor X at low cell density will be tested by isolating and characterizing mutations in the putative repressor gene.