title: The Brucella suis virB operon is induced intracellularly in macrophages.
abstract: A type IV secretion system similar to the VirB system of the phytopathogen Agrobacterium tumefaciens is essential for the intracellular survival and multiplication of the mammalian pathogen Brucella. Reverse transcriptase-PCR showed that the 12 genes encoding the Brucella suis VirB system form an operon. Semiquantitative measurements of virB mRNA levels by slot blotting showed that transcription of the virB operon, but not the flanking genes, is regulated by environmental factors in vitro. Flow cytometry used to measure green fluorescent protein expression from the virB promoter confirmed the data from slot blots. Fluorescence-activated cell sorter analysis and fluorescence microscopy showed that the virB promoter is induced in macrophages within 3 h after infection. Induction only occurred once the bacteria were inside the cells, and phagosome acidification was shown to be the major signal inducing intracellular expression. Because phagosome acidification is essential for the intracellular multiplication of Brucella, we suggest that it is the signal that triggers the secretion of unknown effector molecules. These effector molecules play a role in the remodeling of the phagosome to create the unique intracellular compartment in which Brucella replicates.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, Unité 431, Faculté de Médecine, 30900 Nîmes, France.
authors.forename: Maria Laura
authors.initials: ML
authors.lastname: Boschiroli
authors.forename: Safia
authors.initials: S
authors.lastname: Ouahrani-Bettache
authors.forename: Vincent
authors.initials: V
authors.lastname: Foulongne
authors.forename: Sylvie
authors.initials: S
authors.lastname: Michaux-Charachon
authors.forename: Gisele
authors.initials: G
authors.lastname: Bourg
authors.forename: Annick
authors.initials: A
authors.lastname: Allardet-Servent
authors.forename: Chantal
authors.initials: C
authors.lastname: Cazevieille
authors.forename: Jean Pierre
authors.initials: JP
authors.lastname: Liautard
authors.forename: Michel
authors.initials: M
authors.lastname: Ramuz
authors.forename: David
authors.initials: D
authors.lastname: O'Callaghan
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D002002:Brucella / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008264:Macrophages / Q000382:microbiology*; D008969:Molecular Sequence Data; D009000:Monocytes; D009876:Operon; D010588:Phagosomes / Q000382:microbiology / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014774:Virulence; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D037521:Virulence Factors