A genetic analysis of the function of LuxO, a two-component response regulator involved in quorum sensing in Vibrio harveyi

Two independent quorum-sensing systems control the expression of biolumines cence (lux) in the marine bacterium Vibrio harveyi, Each system is composed of an autoinducer(Al-1 or Al-2) and its cognate sensor (LuxN or LuxQ), The sensors are two-component hybrid kinases, containing both sensor kinase do mains and response regulator domains. Sensory information from the two syst ems is relayed by a phosphotransfer mechanism to a shared integrator protei n called LuxO, LuxO is a member of the response regulator class of the two- component family of signal transduction proteins, and LuxO acts negatively to control luminescence. In this report, missense and in frame deletion mut ations were constructed in luxO that encoded proteins mimicking either the phosphorylated or the unphosphorylated form, and these mutations were intro duced into the V. harveyi chromosome at the luxO locus. Phenotypical analys es of the resulting mutant V, harveyi strains indicate that the phosphoryla ted form of LuxO is the repressor, and that the unphosphorylated form of th e protein is inactive, Analysis of the lux phenotypes of V. harveyi strains containing single and double luxN and luxQ mutations indicate that LuxN an d LuxO have two activities on LuxO. They act as LuxO protein kinases at low cell density in the absence of autoinducers, and they switch to LuxO prote in phosphatases at high cell density in the presence of autoinducers. Furth ermore, the timing and potency of inputs from the two systems into regulati on of quorum sensing are different.