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Journal of Bacteriology, October 2001, p. 5675-5683, Vol. 183, No. 19
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.19.5675-5683.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

External-pH-Dependent Expression of the Maltose Regulon and ompF Gene in Escherichia coli Is Affected by the Level of Glycerol Kinase, Encoded by glpK

Claudia Chagneau, Martine Heyde, Sylvie Alonso,dagger Raymond Portalier, and Patrick Laloi*

Unité de Microbiologie et Génétique, UMR CNRS 5122, Université Lyon 1, F-69622 Villeurbanne Cedex, France

Received 26 March 2001/Accepted 11 July 2001

The expression of the maltose system in Escherichia coli is regulated at both transcriptional and translational levels by the pH of the growth medium (pHo). With glycerol as the carbon source, transcription of malT, encoding the transcriptional activator of the maltose regulon, is weaker in acidic medium than in alkaline medium. malT transcription became high, regardless of the pHo, when glycerol-3-phosphate or succinate was used as the carbon source. Conversely, malT expression was low, regardless of the pHo, when maltose was used as the carbon source. The increase in malT transcription, associated with the pHo, requires the presence of glycerol in the growth medium and the expression of the glycerol kinase (GlpK). Changes in the level of glpK transcription had a great effect on malT transcription. Indeed, a glpFKX promoter-down mutation has been isolated, and in the presence of this mutation, malT expression was increased. When glpK was expressed from a high-copy-number plasmid, the glpK-dependent reduced expression of the maltose system became effective regardless of the pHo. Analysis of this repression showed that a malTp1 malTp10 promoter, which is independent of the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex, was no longer repressed by glpFKX amplification. Thus, GlpK-dependent repression of the maltose system requires the cAMP-CRP complex. We propose that the pHo may affect a complex interplay between GlpK, the phosphotransferase-mediated uptake of glucose, and the adenylate cyclase.

* Corresponding author. Mailing address: Unité de Microbiologie et Génétique, UMR CNRS 5122, Bât A. Lwoff, Université Lyon 1, F-69622 Villeurbanne Cedex, France. Phone: (33) 472 431 621. Fax: (33) 472 432 686. E-mail: plaloi{at}biomserv.univ-lyon1.fr.

dagger Present address: INSERM U447, Institut de Biologie de Lille, Institut Pasteur de Lille, F-59019 Lille Cedex, France.

Journal of Bacteriology, October 2001, p. 5675-5683, Vol. 183, No. 19
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.19.5675-5683.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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