Malott, Rebecca J. O'Grady, Eoin P. Toller, Jessica Inhülsen, Silja Eberl, Leo Sokol, Pamela A. <jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Burkholderia cenocepacia</jats:italic> utilizes quorum sensing to control gene expression, including the expression of genes involved in virulence. In addition to CepR and CciR, a third LuxR homolog, CepR2, was found to regulate gene expression and virulence factor production. All <jats:italic>B. cenocepacia</jats:italic> strains examined contained this orphan LuxR homolog, which was not associated with an adjacent <jats:italic>N</jats:italic>-acyl-homoserine lactone synthase gene. Expression of <jats:italic>cepR2</jats:italic> was negatively autoregulated and was negatively regulated by CciR in strain K56-2. Microarray analysis and quantitative reverse transcription-PCR determined that CepR2 did not influence expression of <jats:italic>cepIR</jats:italic> or <jats:italic>cciIR</jats:italic>. However, in strain K56-2, CepR2 negatively regulated expression of several known quorum-sensing-controlled genes, including genes encoding zinc metalloproteases. CepR2 exerted positive and negative regulation on genes on three chromosomes, including strong negative regulation of a gene cluster located adjacent to <jats:italic>cepR2</jats:italic>. In strain H111, which lacks the CciIR quorum-sensing system, CepR2 positively regulated pyochelin production by controlling transcription of one of the operons required for the biosynthesis of the siderophore in an <jats:italic>N</jats:italic>-acyl-homoserine lactone-independent manner. CepR2 activation of a <jats:italic>luxI</jats:italic> promoter was demonstrated in a heterologous <jats:italic>Escherichia coli</jats:italic> host, providing further evidence that CepR2 can function in the absence of signaling molecules. This study demonstrates that the orphan LuxR homolog CepR2 contributes to the quorum-sensing regulatory network in two distinct strains of <jats:italic>B. cenocepacia</jats:italic>.</jats:p> application/pdf https://sonar.ch/global/documents/255989 eng info:eu-repo/semantics/altIdentifier/doi/10.1128/jb.01746-08 info:eu-repo/semantics/altIdentifier/issn/0021-9193 info:eu-repo/semantics/openAccess Journal of Bacteriology. - American Society for Microbiology. - 2009, vol. 191, no. 8, p. 2447-2460 Molecular Biology Microbiology A Burkholderia cenocepacia Orphan LuxR Homolog Is Involved in Quorum-Sensing Regulation http://purl.org/coar/resource_type/c_6501