Expression of Outer Membrane Proteins in Escherichia coli Growing at Acid pH

Abstract

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.

Bacterial strategies to inhabit acidic environments.

“…Recent data obtained by our group suggests that the binding affinity of OmpRPi to the regulatory region of ompC increases at low pH, resulting in elevated OmpC expression at a low level of OmpR-Pi under hypo-osmosis (unpublished results). Porins were found to be essential for the growth of E. coli in the presence of limited amounts of nutrients at acid pH, but not at high pH (Sato et al, 2000). Therefore this differential regulation of porin expression at different pH values is quite significant for bacterial physiology.…”

“…OmpC is expressed under hyperosmosis, and the level of OmpF decreases with the increase in external osmolarity in neutral and alkaline media. In contrast at high pH, both OmpC and OmpF are expressed in medium containing minimum amounts of nutrients for growth, and the expression of both porins decreases under hyperosmotic stress at acid pH below 6 (Sato et al, 2000). Porin expression correlates with the level of phosphorylated OmpR (OmpR-Pi), which is controlled by phosphorylation and dephosphorylation via EnvZ, a sensor of external osmolarity (Csonka, 1989;Mizuno and Mizushima, 1990;Nikaido and Vaara, 1985).…”

“…The levels are also affected by medium pH (Heyde and Portalier, 1987;Heyde et al, 2000;Sato et al, 2000;Thomas and Booth, 1992). OmpC is expressed under hyperosmosis, and the level of OmpF decreases with the increase in external osmolarity in neutral and alkaline media.…”

The Role of OmpC and OmpF in Acidic Resistance in Escherichia coli

“…22,23) OmpC and OmpF play important roles in the membrane transport of solutes, such as amino acids, in E. coli and other Gram-negative bacteria. 24) However, an E. coli mutant that was deficient in both ompC and ompF was shown to grow under conventional growth conditions.…”

Amino terminus mutant OmpA from an isolated antibiotic resistant <i>Escherichia</i> <i>coli</i> still possess resistance to environmental stresses

“…vironmental stress were consequently identified based on previous literatures with slight modification [24][25][26]. For all the experimental analysis, the expressed cell cultures were adjusted OD 600 to 0.7 and subsequently diluted 10 5 -fold with LB media.…”