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Effects of changes in membrane sodium flux on virulence gene expression in Vibrio cholerae.
|Title||Effects of changes in membrane sodium flux on virulence gene expression in Vibrio cholerae.|
|Publication Type||Journal Article|
|Year of Publication||1999|
|Authors||Häse CC, Mekalanos JJ|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Date Published||1999 Mar 16|
|Keywords||Bacterial Proteins, beta-Galactosidase, Cell Membrane, Cholera, DNA-Binding Proteins, Gene Expression Regulation, Bacterial, Genes, Reporter, Ion Transport, Membrane Proteins, Mutation, Sodium, Transcription Factors, Vibrio cholerae, Virulence|
The expression of several virulence factors of Vibrio cholerae is coordinately regulated by the ToxT molecule and the membrane proteins TcpP/H and ToxR/S, which are required for toxT transcription. To identify proteins that negatively affect toxT transcription, we screened transposon mutants of V. cholerae carrying a chromosomally integrated toxT::lacZ reporter construct for darker blue colonies on media containing 5-bromo-4-chlor-3-indolyl beta-D galactoside (X-gal). Two mutants had transposon insertions in a region homologous to the nqr gene cluster of Vibrio alginolyticus, encoding a sodium-translocating NADH-ubiquinone oxidoreductase (NQR). In V. alginolyticus, NQR is a respiration-linked Na+ extrusion pump generating a sodium motive force that can be used for solute import, ATP synthesis, and flagella rotation. Inhibition of NQR enzyme function in V. cholerae by the specific inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO) resulted in elevated toxT::lacZ activity. Increased toxT::lacZ expression in an nqr mutant strain compared with the parental strain was observed when the TcpP/H molecules alone were strongly expressed, suggesting that the negative effect of the NQR complex on toxT transcription is mediated through TcpP/H. However, the ability of the TcpP/H proteins to activate the toxT::lacZ reporter construct was greatly diminished in the presence of high NaCl concentrations in the growth medium. The flagellar motor of V. cholerae appears to be driven by a sodium motive force, and modulation of flagella rotation by inhibitory drugs, high media viscosity, or specific mutations resulted in increases of toxT::lacZ expression. Thus, the regulation of the main virulence factors of V. cholerae appears to be modulated by endogenous and exogenous sodium levels in a complex way.
|Alternate Journal||Proc. Natl. Acad. Sci. U.S.A.|