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Infection and Immunity, March 2000, p. 1491-1497, Vol. 68, No. 3
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Virulence Regulatory Protein ToxR Mediates Enhanced Bile
Resistance in Vibrio cholerae and Other Pathogenic
Vibrio Species
Daniele
Provenzano,
Darren A.
Schuhmacher,
Justin L.
Barker, and
Karl E.
Klose*
Department of Microbiology, University of
Texas Health Science Center, San Antonio, Texas 78284-7758
Received 1 October 1999/Returned for modification 12 November
1999/Accepted 7 December 1999
The transmembrane regulatory protein ToxR is required for
expression of virulence factors in the human diarrheal pathogen Vibrio cholerae, including cholera toxin (CT) and the toxin
coregulated pilus (TCP). ToxR is necessary for transcription of the
gene encoding a second regulatory protein, ToxT, which is the direct
transcriptional activator of CT and TCP genes. However, ToxR,
independent of ToxT, directly activates and represses transcription of
the outer membrane porins OmpU and OmpT, respectively. The genes
encoding TCP and CT (and including ToxT) lie on horizontally acquired
genetic elements, while the toxR, ompU, and
ompT genes are apparently in the ancestral Vibrio chromosome. The contribution of ToxR-dependent
modulation of outer membrane porins to cholera pathogenesis has
remained unknown. We demonstrate that ToxR mediates enhanced bile
resistance in a ToxT-independent manner. In both classical and El Tor
biotypes of V. cholerae, a toxR mutant strain
has a reduced minimum bactericidal concentration (MBC) of bile, the
bile component deoxycholate (DC), and the anionic detergent sodium
dodecyl sulfate (SDS) compared to both wild-type and toxT
mutant strains. Classical and El Tor toxR mutant strains
also exhibit reduced growth rates at subinhibitory concentrations of DC
and SDS. Growth of either V. cholerae biotype in
subinhibitory concentrations of bile or DC induces increased ToxR-dependent production of a major 38-kDa outer membrane protein, which was confirmed to be OmpU by Western blot. Measurement of transcription of a ompUp-lacZ fusion in both
biotypes reveals stimulation (about two- to threefold) of
ToxR-dependent ompU transcription by the presence of bile
or DC, suggesting that ToxR may respond to the presence of bile. The
toxR mutant strains of three additional human intestinal
pathogenic Vibrio species, V. mimicus, V. fluvialis, and V. parahaemolyticus, display lower
MBCs of bile, DC, and SDS and have altered outer membrane protein
profiles compared to the parental wild-type strains. Our results
demonstrate a conserved role for ToxR in the modulation of outer
membrane proteins and bile resistance of pathogenic Vibrio
species and suggest that these ToxR-dependent outer membrane proteins
may mediate enhanced resistance to bile. We speculate that
ToxR-mediated bile resistance was an early step in the evolution of
V. cholerae as an intestinal pathogen.
*
Corresponding author. Mailing address: Department of
Microbiology, University of Texas Health Science Center, 7703 Floyd
Curl Dr., San Antonio, TX 78284-7758. Phone: (210) 567-3990. Fax: (210) 567-6612. E-mail: klose{at}uthscsa.edu.
Infection and Immunity, March 2000, p. 1491-1497, Vol. 68, No. 3
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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