title: Control of the type 3 secretion system in Vibrio harveyi by quorum sensing through repression of ExsA.
abstract: The type 3 secretion system (T3SS) genes of Vibrio harveyi are activated at low cell density and repressed at high cell density by quorum sensing (QS). Repression requires LuxR, the master transcriptional regulator of QS-controlled genes. Here, we determine the mechanism underlying the LuxR repression of the T3SS system. Using a fluorescence-based cell sorting approach, we isolated V. harveyi mutants that are unable to express T3SS genes at low cell density and identified two mutations in the V. harveyi exsBA operon. While LuxR directly represses the expression of exsBA, complementation and epistasis analyses reveal that it is the repression of exsA expression, but not exsB expression, that is responsible for the QS-mediated repression of T3SS genes at high cell density. The present work further defines the genes in the V. harveyi QS regulon and elucidates a mechanism demonstrating how multiple regulators can be linked in series to direct the expression of QS target genes specifically at low or high cell density.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Waters
authors.forename: Julie T
authors.initials: JT
authors.lastname: Wu
authors.forename: Meghan E
authors.initials: ME
authors.lastname: Ramsey
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Harris
authors.forename: Bonnie L
authors.initials: BL
authors.lastname: Bassler
mesh_terms: D001426:Bacterial Proteins / Q000037:antagonists & inhibitors*; D017353:Gene Deletion; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000096:biosynthesis*; D053038:Quorum Sensing; D012097:Repressor Proteins / Q000378:metabolism*; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D014733:Vibrio / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; C095092:ExsA protein, bacteria; D026901:Membrane Transport Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; C064778:LuxR autoinducer binding proteins