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J. Bacteriol., 11 1996, 6487-6495, Vol 178, No. 22
GM Young, D Amid and VL Miller
To infect a susceptible host, the gastrointestinal pathogen Yersinia
enterocolitica must survive passage through the acid environment of the
stomach. In this study, we showed that Y. enterocolitica serotype O8
survives buffered acidic conditions as low as pH 1.5 for long periods of
time provided urea is available. Acid tolerance required an unusual
cytoplasmically located urease that was activated 780-fold by low-pH
conditions. Acid tolerance of Helicobacter species has also been attributed
to urease activity, but in that case urease was not specifically activated
by low-pH conditions. A ure mutant strain of Y. enterocolitica was
constructed which was hypersensitive to acidic conditions when urea was
available and, unlike the parental strain, was unable to grow when urea was
the sole nitrogen source. Examination of other urease-producing
gram-negative bacteria indicated that Morganella morganii survives in
acidic conditions but Escherichia coli 1021, Klebsiella pneumoniae, Proteus
mirabilis, Providencia stuartii, and Pseudomonas aeruginosa do not.
Consistent with these results, biochemical evidence demonstrated that Y.
enterocolitica and M. morganii ureases were activated in vitro by low pH
with an unusually low activity optimum of pH 5.5. In whole cells activation
occurred as medium values decreased below pH 3.0 for Y. enterocolitica and
pH 5.5 for M. morganii, suggesting that in vivo activation occurs as a
result of cytoplasmic acidification. DNA sequence analysis of portions of
the M. morganii ure locus showed that the predicted primary structure of
the enzyme structural subunits is most similar to those of Y.
enterocolitica urease. One region of similarity between these two ureases
located near the active site is distinct from most other ureases but is
present in the urease of Lactobacillus fermentum. This region of similarity
may be responsible for the unique properties of the Y. enterocolitica and
M. morganii ureases since the L. fermentum urease also has been shown to
have a low pH optimum for activity.
Copyright © 1996, American Society for Microbiology
A bifunctional urease enhances survival of pathogenic Yersinia enterocolitica and Morganella morganii at low pH
Department of Microbiology and Molecular Genetics, University of California, Los Angeles, 90095, USA.
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