RESUMO
In Escherichia coli membranes, three major phospholipids are formed: phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL). We report here the survival of mutants lacking either PE or both PG and CL at an acid pHo and during long-term survival experiments. Stationary phase cultures of E. coli lacking PE are much more sensitive to acid shock (pHo 3) than the wild-type strain. Moreover, in the strain lacking PE, long-term survival in stationary phase is impaired and after 5 days no viable cells are recovered. The survival of an exponential phase culture to acid shock is known to be increased if the culture is exposed to moderately acid conditions (pHo 5) prior to a shift to pHo 3. If either PE or both PG and CL are missing, the exposure to pHo 5 does not increase the survival at pHo 3.
Assuntos
Adaptação Fisiológica , Escherichia coli/fisiologia , Fosfolipídeos/fisiologia , CDPdiacilglicerol-Serina O-Fosfatidiltransferase/genética , CDPdiacilglicerol-Serina O-Fosfatidiltransferase/metabolismo , Cardiolipinas/fisiologia , Membrana Celular/química , Contagem de Colônia Microbiana , Escherichia coli/genética , Escherichia coli/crescimento & desenvolvimento , Escherichia coli/metabolismo , Concentração de Íons de Hidrogênio , Mutagênese Insercional , Fosfatidiletanolaminas/fisiologia , Fosfatidilgliceróis/fisiologia , Transferases (Outros Grupos de Fosfato Substituídos)/genética , Transferases (Outros Grupos de Fosfato Substituídos)/metabolismoRESUMO
The Escherichia coli maltose regulon consists of five operons under the control of the MalT transcriptional activator. lac operon fusions were constructed in vitro with the MalT-dependent promoter and with the malT promoter itself. beta-Galactosidase activity displayed by these fusions during growth at different external pH (pHo) revealed that growth at a pHo higher than 6 stimulates the transcription of malT- and MalT-controlled genes in the absence or presence of maltose. Using a malTp1 malTp10 promoter that is cAMP-CRP (cAMP receptor protein)-independent, it was demonstrated that CRP is essential for malT pHo regulation and that the pHo-dependent activity of malKp is a direct consequence of malT regulation. The pHo regulation displayed by a deleted but still functional malT promoter fused to lacZ demonstrates that this minimal promoter contains all the regulatory regions for establishing pHo regulation. In the absence of MIc, a repressor of malT expression, the pHo regulation of malT was still effective. It is proposed that binding of cAMP-CRP at malTp may be affected by malTp topology induced by pHo or that a pHo-dependent effector may act in concert with the cAMP-CRP complex.