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Journal of Bacteriology, June 2001, p. 3652-3662, Vol. 183, No. 12
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.12.3652-3662.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of the Role of the
ToxR-Modulated Outer Membrane Porins OmpU and OmpT in
Vibrio cholerae Virulence
Daniele
Provenzano,
Crystal
M.
Lauriano, and
Karl E.
Klose*
Department of Microbiology, University of
Texas Health Science Center, San Antonio, Texas 78229-3900
Received 2 February 2001/Accepted 30 March 2001
ToxR, the transmembrane regulatory protein required for expression
of virulence factors in the human diarrheal pathogen Vibrio cholerae, directly activates and represses the transcription of two outer membrane porins, OmpU and OmpT, respectively. In an attempt
to dissect the role of the OmpU and OmpT porins in viability and
virulence factor expression, in-frame chromosomal deletions were
constructed in the coding sequences of ompU and
ompT of V. cholerae. Two separate deletions
were introduced into ompU; the first (small) deletion,
ompU1, removed the coding sequence for 84 internal amino
acids (aa), while the second (large) deletion,
ompU2,
removed the coding sequence for the entire amino-terminal 274 aa. The
ompU1 strain had a growth defect that could not be complemented by episomal expression of full-length ompU. In
contrast, a strain with
ompU2 displayed wild-type growth
kinetics in rich media, suggesting that this is the true phenotype of a
strain lacking OmpU and that the truncated OmpU protein, rather than the absence of OmpU, may be the cause for the
ompU1
phenotype. A large deletion removing the coding sequence for the entire
N-terminal 273 aa of OmpT (
ompT) was also constructed in
wild-type as well as
toxR and
ompU2
strains, and these strains displayed wild-type growth kinetics in rich
media. However, the
ompU2 strain was deficient for
growth in deoxycholate compared to wild-type,
ompT, and
ompU2
ompT strains, reinforcing a
positive role for the OmpU porin and a negative role for the OmpT porin
in V. cholerae resistance to anionic detergents. The
ompU2,
ompT, and
ompU2
ompT strains exhibited wild-type levels of in vitro
virulence factor expression and resistance to polymyxin B and serum and in vivo colonization levels similar to a wild-type strain in the infant
mouse intestine. Our results demonstrate that (i) OmpU and OmpT are not
essential proteins, as was previously thought; (ii) these porins
contribute to V. cholerae resistance to anionic detergents;
and (iii) OmpU and OmpT are not essential for virulence factor
expression in vitro or intestinal colonization in vivo.
*
Corresponding author. Mailing address: Department of
Microbiology, University of Texas Health Science Center, 7703 Floyd
Curl Dr., San Antonio, TX 78229-3900. Phone: (210) 567-3990. Fax: (210) 567-9231. E-mail: klose{at}uthscsa.edu.

Present address: Department of Microbiology and Molecular Genetics,
Harvard Medical School, Boston, MA
02115.
Journal of Bacteriology, June 2001, p. 3652-3662, Vol. 183, No. 12
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.12.3652-3662.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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