D. Pickard et al., CHARACTERIZATION OF DEFINED OMPR MUTANTS OF SALMONELLA-TYPHI - OMPR IS INVOLVED IN THE REGULATION OF VI POLYSACCHARIDE EXPRESSION, Infection and immunity, 62(9), 1994, pp. 3984-3993
The ompB operon, comprising the ompR and envZ genes, was cloned from a
Salmonella typhi Ty2 cosmid bank and characterized by DNA sequence an
alysis. The S. typhi ompR and envZ genes contained open reading frames
encoding proteins of 240 and 451 amino acids, respectively. Compariso
n with the Salmonella typhimurium OmpB protein sequences revealed 99.5
% homology. The DNA sequence data were used to identify appropriate re
striction sites for generating a defined deletion of 517 bp within the
open reading frame of the ompR gene. This deletion was introduced by
homologous recombination into the chromosomes of two S. typhi strains
which already harbored defined deletions in both the aroC and aroD gen
es. The presence of the deletions within ompR was confirmed by Souther
n hybridization and sequencing of the DNA fragments surrounding the de
leted regions by PCR. The S. typhi ompR mutants displayed a marked dec
rease in OmpC and OmpF porin expression as demonstrated by examination
of outer membrane preparations. It was also found that S. typhi strai
ns harboring the defined ompR deletions no longer agglutinated with Vi
antiserum. However, when a functional ompB operon was introduced back
into the S. typhi ompR mutants, either on a multicopy plasmid or as a
single-copy chromosomal replacement, the Vi(+) phenotype was restored
. The levels of Vi synthesis were also found to be sensitive to differ
ent concentrations of sodium chloride present in the growth medium, al
though the levels of sensitivity varied between different isolates of
S. typhi. It is therefore concluded that the ompR-envZ two component r
egulatory system plays an important role in the regulation of Vi polys
accharide synthesis in S. typhi and that one of the environmental sign
als for this regulation may be osmolarity.