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Applied and Environmental Microbiology, March 2000, p. 943-947, Vol. 66, No. 3
Faculty of Pharmaceutical Sciences, Chiba
University, Inage-ku, Chiba 263-8522, Japan
Received 27 September 1999/Accepted 20 December 1999
It is generally accepted for Escherichia coli that (i)
the level of OmpC increases with increased osmolarity when cells are growing in neutral and alkaline media, whereas the level of OmpF decreases at high osmolarity, and that (ii) the two-component system
composed of OmpR (regulator) and EnvZ (sensor) regulates porin
expression. In this study, we found that OmpC was expressed at low
osmolarity in medium of pH below 6 and that the expression was
repressed when medium osmolarity was increased. In contrast, the
expression of ompF at acidic pH was essentially the same as that at alkaline pH. Neither OmpC nor OmpF was detectable in an ompR mutant at both acid and alkaline pH values. However,
OmpC and OmpF were well expressed at acid pH in a mutant
envZ strain, and their expression was regulated by medium
osmolarity. Thus, it appears that E. coli has a
different mechanism for porin expression at acid pH. A mutant deficient
in ompR grew slower than its parent strain in
low-osmolarity medium at acid pH (below 5.5). The same growth
diminution was observed when ompC and ompF were
deleted, suggesting that both OmpF and OmpC are required for optimal
growth under hypoosmosis at acid pH.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Expression of Outer Membrane Proteins in
Escherichia coli Growing at Acid pH
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Corresponding author. Mailing address: Faculty of
Pharmaceutical Sciences, Chiba University, 1-33, Yayoi-cho, Inage-ku,
Chiba 263-8522, Japan. Phone: 81-43-290-2916. Fax: 81-43-290-2918. E-mail: hiroshi{at}p.chiba-u.ac.jp.
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