title: A λ Cro-Like Repressor Is Essential for the Induction of Conjugative Transfer of SXT/R391 Elements in Response to DNA Damage.
abstract: Integrative and conjugative elements (ICEs) of the SXT/R391 family are the main contributors to acquired multidrug resistance in the seventh pandemic lineage of Vibrio cholerae, the etiological agent of the diarrheal disease cholera. Conjugative transfer of SXT/R391 ICEs is triggered by antibiotics and agents promoting DNA damage through RecA-dependent autoproteolysis of SetR, an ICE-encoded λ CI-like repressor. Here, we describe the role of CroS, a distant λ Cro homolog, as a key component contributing to the regulation of expression of the activator SetCD that orchestrates the expression of the conjugative transfer genes. We show that deletion of croS abolishes the SOS response-dependent induction of SXT despite the presence of a functional setR gene. Using quantitative reverse transcription-PCR and lacZ reporter assays, we also show that CroS represses setR and setCD expression by binding to operator sites shared with SetR. Furthermore, we provide evidence of an additional operator site bound by SetR and CroS. Finally, we show that SetCD expression generates a positive feedback loop due to SXT excision and replication in a fraction of the cell population. Together, these results refine our understanding of the genetic regulation governing the propagation of major vectors of multidrug resistance.
  
  
  OBJECTIVE
  Healthcare systems worldwide are challenged by an alarming drug resistance crisis caused by the massive and rapid propagation of antibiotic resistance genes and the associated emergence of multidrug-resistant pathogenic bacteria. SXT/R391 ICEs contribute to this phenomenon not only in clinical and environmental vibrios but also in several members of the family Enterobacteriaceae. We have identified and characterized here the regulator CroS as a key factor in the stimulation of conjugative transfer of these ICEs in response to DNA-damaging agents. We have also untangled conflicting evidence regarding autoactivation of transfer by the master activator of SXT/R391 ICEs, SetCD. Discovery of CroS provides a clearer and more complete understanding of the regulatory network that governs the dissemination of SXT/R391 ICEs in bacterial populations.
authors.affiliation: Laboratory of Bacterial Molecular Genetics, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Dominic
authors.initials: D
authors.lastname: Poulin-Laprade
authors.affiliation: Laboratory of Bacterial Molecular Genetics, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada Vincent.Burrus@USherbrooke.ca.
authors.forename: Vincent
authors.initials: V
authors.lastname: Burrus
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D010582:Bacteriophage lambda / Q000235:genetics; D003227:Conjugation, Genetic / Q000235:genetics*; D004249:DNA Damage / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D008969:Molecular Sequence Data; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D013014:SOS Response, Genetics / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014734:Vibrio cholerae / Q000235:genetics*; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins