Affiliation:
1. Department of Microbiology, University of Texas Health Science Center, San Antonio, Texas 78284-7758
Abstract
ABSTRACT
The regulatory protein ToxT directly activates the transcription of virulence factors in
Vibrio cholerae
, including cholera toxin (CT) and the toxin-coregulated pilus (TCP). Specific environmental signals stimulate virulence factor expression by inducing the transcription of
toxT
. We demonstrate that transcriptional activation by the ToxT protein is also modulated by environmental signals. ToxT expressed from an inducible promoter activated high-level expression of CT and TCP in
V. cholerae
at 30°C, but expression of CT and TCP was significantly decreased or abolished by the addition of 0.4% bile to the medium and/or an increase of the temperature to 37°C. Also, expression of six ToxT-dependent Tn
phoA
fusions was modulated by temperature and bile. Measurement of ToxT-dependent transcription of genes encoding CT and TCP by
ctxAp
- and
tcpAp
-luciferase fusions confirmed that negative regulation by 37°C or bile occurs at the transcriptional level in
V. cholerae
. Interestingly, ToxT-dependent transcription of these same promoters in
Salmonella typhimurium
was relatively insensitive to regulation by temperature or bile. These data are consistent with ToxT transcriptional activity being modulated by environmental signals in
V. cholerae
and demonstrate an additional level of complexity governing the expression of virulence factors in this pathogen. We propose that negative regulation of ToxT-dependent transcription by environmental signals prevents the incorrect temporal and spatial expression of virulence factors during cholera pathogenesis.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
135 articles.
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