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A genetic analysis of the functions of LuxN: a two‐component hybrid sensor kinase that regulates quorum sensing in Vibrio harveyi
Author(s) -
Freeman Jeremy A.,
Lilley Brendan N.,
Bassler Bonnie L.
Publication year - 2000
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2000.01684.x
Subject(s) - vibrio harveyi , response regulator , histidine kinase , biology , quorum sensing , phosphatase , autoinducer , kinase , two component regulatory system , microbiology and biotechnology , regulator , luciferase , phosphorylation , gene , vibrio , genetics , virulence , bacteria , transfection , mutant
The bioluminescent marine bacterium Vibrio harveyi controls light production using two parallel quorum‐sensing systems. V. harveyi produces two autoinducers (AI‐1 and AI‐2), which are recognized by cognate membrane‐bound two‐component hybrid sensor kinases called LuxN and LuxQ respectively. Under conditions of low cell density, in the absence of autoinducer, the hybrid sensors are kinases, and under conditions of high cell density, in the presence of autoinducer, the sensors are phosphatases. These activities allow LuxN and LuxQ to modulate the level of phosphorylation of the response regulator protein LuxO. LuxO, in turn, controls the transcription of the genes encoding luciferase. The phosphorelay protein LuxU is required for signalling to LuxO. In this report, we present a genetic analysis of the activities of the AI‐1 sensor LuxN. Point mutations and in frame deletions were constructed in luxN and recombined onto the chromosome of V. harveyi for in vivo phenotypic analysis. We show that the conserved histidine (H471) in the sensor kinase domain of LuxN is required for kinase activity but not for phosphatase activity. In contrast, the conserved aspartate (D771) in the response regulator domain of LuxN is required for both activities. Furthermore, the LuxN phosphatase activity is localized to the response regulator domain. Our results indicate that the LuxN kinase activity is regulated by the presence of AI‐1, whereas the LuxN phosphatase activity is constitutive. We also show that signalling from the two V. harveyi quorum‐sensing systems is not equivalent. AI‐1 and LuxN have a much greater effect on the level of LuxO phosphate and therefore Lux expression than do AI‐2 and LuxQ.