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 du ring growth at different external pHs (pHo) as a function of the acetyl pho sphate (AcP) level (Delta ackA pta or ackA mutant, pyruvate or glucose as t he 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 a mount of OmpR-P and subsequent pao-dependent expression of ompF and ompC. W e also propose the existence of a specific signal, independent of EnvZ and AcP, leading to OmpR phosphorylation in response to pyruvate.