Salicylate inhibits the translation and transcription of ompF in Escherichia coli

OmpF is a major outer membrane protein in Escherichia coli whose expression is regulated by a large number of factors, including the osmolarity of the growth medium and the concentration of salicylate. We have previously shown that at low osmolarity, OmpF is post-transcriptionally regulated by micF mRNA, and that at high osmolarity, regulation occurs primarily by the inhibition of transcription by OmpR (Ramani et al. 1994). In contrast, salicylate was reported to alter OmpF expression solely by blocking translation primarily through micF mRNA (Rosner et al. 1991). We examined the effect of salicylate by analyzing the levels of OmpF in wild-type and micF– strains grown with salicylate. At low concentrations of salicylate (0–4 mM), OmpF levels were inhibited strongly in wild-type cells, whereas no inhibition of OmpF was observed in the micF– strain. At high concentrations of salicylate (10–20 mM), both the wild type and the micF– strain showed strong inhibition of OmpF. To study the effect of salicylate on transcription, ompF mRNA and micF mRNA were analyzed in wild-type cells. micF mRNA levels increased during growth with 1, 2, and 4 mM salicylate. In contrast, ompF mRNA levels were not affected by low concentrations of salicylate, but decreased strongly at 10 and 20 mM salicylate. Taken together, these results suggest that similar to osmoregulation, salicylate inhibits both the translation and transcription of ompF.Key words: salicylate, OmpF, micF, osmoregulation.