Involvement of carbon source and acetyl phosphate in the external-pH-dependent expression of porin genes in Escherichia coli.

The porin composition of the Escherichia coli cell envelope was analyzed during growth at different external pHs (pHo) as a function of the acetyl phosphate (AcP) level (ΔackA pta or ackA mutant, pyruvate or glucose as the carbon source) in the presence or absence of EnvZ. Our results indicate that the AcP level is influenced by the pHo, leading to modulation of the amount of OmpR-P and subsequent pHo-dependent expression of ompF and ompC. We also propose the existence of a specific signal, independent of EnvZ and AcP, leading to OmpR phosphorylation in response to pyruvate.