Individual and combined roles of the master regulators AphA and LuxR in control of the Vibrio harveyi quorum-sensing regulon. Author Julia van Kessel, Steven Rutherford, Yi Shao, Alan Utria, Bonnie Bassler Publication Year 2013 Type Journal Article Abstract Bacteria use a chemical communication process called quorum sensing to control transitions between individual and group behaviors. In the Vibrio harveyi quorum-sensing circuit, two master transcription factors, AphA and LuxR, coordinate the quorum-sensing response. Here we show that AphA regulates 167 genes, LuxR regulates 625 genes, and they coregulate 77 genes. LuxR strongly controls genes at both low cell density and high cell density, suggesting that it is the major quorum-sensing regulator. In contrast, AphA is absent at high cell density and acts to fine-tune quorum-sensing gene expression at low cell density. We examined two loci as case studies of coregulation by AphA and LuxR. First, AphA and LuxR directly regulate expression of the genes encoding the quorum-regulatory small RNAs Qrr2, Qrr3, and Qrr4, the consequence of which is a specifically timed transition between the individual and the group life-styles. Second, AphA and LuxR repress type III secretion system genes but at different times and to different extents. The consequence of this regulation is that type III secretion is restricted to a peak at mid-cell density. Thus, the asymmetric production of AphA and LuxR coupled with differences in their strengths and timing of target gene regulation generate a precise temporal pattern of gene expression. Keywords Gene Expression Regulation, Bacterial, Quorum Sensing, Repressor Proteins, Trans-Activators, Vibrio, Escherichia coli, Transcription Factors, Regulon, Cell Proliferation, Mutation, Protein Array Analysis, Real-Time Polymerase Chain Reaction, Time Factors Journal J Bacteriol Volume 195 Issue 3 Pages 436-43 Date Published 2013 Feb ISSN Number 1098-5530 DOI 10.1128/JB.01998-12 Alternate Journal J Bacteriol PMCID PMC3554009 PMID 23204455 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML