Regulation of ompF porin expression by salicylate in Escherichia coli

Abstract

The expression of ompF, the gene encoding a major outer membrane protein of Escherichia coli, is regulated by various environmental factors. The mechanism by which salicylate (SAL) drastically reduces ompF expression was studied here by means of lacZ fusions to ompF, ompC, and micF, by sodium dodecyl sulfate-gel electrophoresis of outer membrane proteins, and by measurements of outer membrane permeability. Growth of E. coli in LB broth containing SAL strongly reduced ompF-specific translation of an ompF-lacZ fusion. The extent of this reduction varied with the SAL concentration from 64% at 0.5 mM to 95% at 2 mM and greater than 99% at 10 mM. ompF-lacZ transcription was not affected by SAL, whereas ompC-lacZ transcription was elevated by 70%. Since the micF transcript is antisense to a portion of the ompF transcript and is capable of decreasing the translation of ompF, the effect of SAL on micF transcription was measured in a micF-lacZ fusion strain. SAL-grown cells contained three- to fourfold more micF transcript during the logarithmic phase of growth than did the control cultures. However, micF was not absolutely required for the response to SAL. In micF-deleted strains, the effects of SAL on ompF translation, on OmpF in the outer membrane, and on outer membrane permeability were diminished but still evident. The effect of SAL on ompF expression was independent of the osmolarity of the medium and was epistatic to certain ompB regulatory mutations: the high levels of ompF expression found in envZ3 and ompR472 strains were greatly reduced by growth in SAL. Unexpectedly, the OmpC- phenotypes of these mutants were suppressed by SAL. Thus, growth in SAL severely decreases the translation of ompF while enhancing the transcription of micF and ompC. In this respect, SAL-grown cells resemble certain marA and tolC mutants that have high levels of micF and ompC transcripts and low levels of OmpF.