title: An operon of three transcriptional regulators controls horizontal gene transfer of the integrative and conjugative element ICEclc in Pseudomonas knackmussii B13.
abstract: The integrative and conjugative element ICEclc is a mobile genetic element in Pseudomonas knackmussii B13, and an experimental model for a widely distributed group of elements in Proteobacteria. ICEclc is transferred from specialized transfer competent cells, which arise at a frequency of 3-5% in a population at stationary phase. Very little is known about the different factors that control the transfer frequency of this ICE family. Here we report the discovery of a three-gene operon encoded by ICEclc, which exerts global control on transfer initiation. The operon consists of three consecutive regulatory genes, encoding a TetR-type repressor MfsR, a MarR-type regulator and a LysR-type activator TciR. We show that MfsR autoregulates expression of the operon, whereas TciR is a global activator of ICEclc gene expression, but no clear role was yet found for MarR. Deletion of mfsR increases expression of tciR and marR, causing the proportion of transfer competent cells to reach almost 100% and transfer frequencies to approach 1 per donor. mfsR deletion also caused a two orders of magnitude loss in population viability, individual cell growth arrest and loss of ICEclc. This indicates that autoregulation is an important feature maintaining ICE transfer but avoiding fitness loss. Bioinformatic analysis showed that the mfsR-marR-tciR operon is unique for ICEclc and a few highly related ICE, whereas tciR orthologues occur more widely in a large variety of suspected ICE among Proteobacteria.
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Pradervand
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Sandra
authors.initials: S
authors.lastname: Sulser
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: François
authors.initials: F
authors.lastname: Delavat
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Ryo
authors.initials: R
authors.lastname: Miyazaki
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Iker
authors.initials: I
authors.lastname: Lamas
authors.affiliation: Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Jan Roelof
authors.initials: JR
authors.lastname: van der Meer
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D055786:Gene Knockout Techniques; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D011401:Promoter Regions, Genetic; D011549:Pseudomonas / Q000235:genetics*; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D012097:Repressor Proteins; D015534:Trans-Activators