The Brucella suis virB operon is induced intracellularly in macrophages.
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.
Boschiroli
Maria Laura
ML
Institut National de la Santé et de la Recherche Médicale, Unité 431, Faculté de Médecine, 30900 Nîmes, France.
Ouahrani-Bettache
Safia
S
Foulongne
Vincent
V
Michaux-Charachon
Sylvie
S
Bourg
Gisele
G
Allardet-Servent
Annick
A
Cazevieille
Chantal
C
Liautard
Jean Pierre
JP
Ramuz
Michel
M
O'Callaghan
David
D
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
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D037521:Virulence Factors