title: Roles for DNA supercoiling and the Fis protein in modulating expression of virulence genes during intracellular growth of Salmonella enterica serovar Typhimurium.
abstract: Adaptation of bacterial pathogens to an intracellular environment requires resetting of the expression levels of a wide range of both virulence and housekeeping genes. We investigated the possibility that changes in DNA supercoiling could modulate the expression of genes known to be important in the intracellular growth of the pathogen Salmonella enterica serovar Typhimurium. Our data show that DNA becomes relaxed when Salmonella grows in murine macrophage but not in epithelial cells, indicating that DNA supercoiling plays a role in discrimination between two types of intracellular environment. The ssrA regulatory gene within the SPI-2 pathogenicity island that is required for survival in macrophage was found to be upregulated by DNA relaxation. This enhancement of expression also required the Fis nucleoid-associated protein. Manipulating the level of the Fis protein modulated both the level of DNA supercoiling and ssrA transcription. We discuss a model of bacterial intracellular adaptation in which Fis and DNA supercoiling collaborate to fine-tune virulence gene expression.
authors.affiliation: Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, Ireland.
authors.forename: Tadhg
authors.initials: T
authors.lastname: O Cróinín
authors.forename: Ronan K
authors.initials: RK
authors.lastname: Carroll
authors.forename: Arlene
authors.initials: A
authors.lastname: Kelly
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Dorman
mesh_terms: D000818:Animals; D002460:Cell Line; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D004847:Epithelial Cells / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands; D007700:Kinetics; D008264:Macrophages / Q000166:cytology / Q000382:microbiology; D051379:Mice; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000235:genetics; D012486:Salmonella typhimurium / Q000254:growth & development* / Q000472:pathogenicity*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014774:Virulence / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D012329:RNA, Bacterial; D014157:Transcription Factors; C096222:tmRNA