Loss of Osmoregulation of OmpC Porin Occurs if Escherichia coli are Deficient in cAMP Receptor Protein

In Escherichia coli, the regulator OmpR and EnvZ respond to cyclic AMP and are directly responsible for the regulation of outer membrane porin proteins OmpC and OmpF. We observe that increasing levels of OmpC expression in wildtype strains exposed to increasing osmotic pressure. However, Δ crp strains deficient in cyclic AMP receptor protein (CRP) showed significantly lower levels of OmpC and the OmpC protein level remained stable with increased osmotic pressure. This observation is consistent with previously proposed osmoregulation pathway, and confirm the importance of cAMP receptor protein in osmoregulation.