NDLI: pH-Dependent Modulation of Cyclic AMP Levels and GadW-Dependent Repression of RpoS Affect Synthesis of the GadX Regulator and Escherichia coli Acid Resistance

Content Provider	PubMed Central
Author	Ma, Zhuo Richard, Hope Foster, John W.
Copyright Year	2003
Abstract	Extreme acid resistance is a remarkable property of virulent and avirulent Escherichia coli. The ability to resist environments in which the pH is 2.5 and below is predicted to contribute significantly to the survival of E. coli during passage through the gastric acid barrier. One acid resistance system imports glutamate from acidic environments and uses it as a proton sink during an intracellular decarboxylation reaction. Transcription of the genes encoding the glutamate decarboxylases and the substrate-product antiporter required for this system is induced under a variety of conditions, including the stationary phase and a low pH. Acid induction during log-phase growth in minimal medium appears to occur through multiple pathways. We recently demonstrated that GadE, the essential activator of the genes, was itself acid induced. In this report we present evidence that there is a regulatory loop involving cross-repression of two AraC-like regulators, GadX and GadW, that can either assist or interfere with GadE activation of the gad decarboxylase and antiporter genes, depending on the culture conditions. Balancing cross-repression appears to be dependent on cAMP and the cAMP regulator protein (CRP). The control loop involves the GadX protein repressing the expression of gadW and the GadW protein repressing or inhibiting RpoS, which is the alternative sigma factor that drives transcription of gadX. CRP and cAMP appear to influence GadX-GadW cross-repression from outside the loop by inhibiting production of RpoS. We found that GadW represses the decarboxylase genes in minimal medium and that growth under acidic conditions lowers the intracellular cAMP levels. These results indicate that CRP and cAMP can mediate pH control over gadX expression and, indirectly, expression of the decarboxylase genes. Mutational or physiological lowering of cAMP levels increases the level of RpoS and thereby increases the production of GadX. Higher GadX levels, in turn, repress gadW and contribute to induction of the gad decarboxylase genes. The presence of multiple pH control pathways governing expression of this acid resistance system is thought to reflect different environmental routes to a low pH.
Related Links	http://dx.doi.org/10.1128/jb.185.23.6852-6859.2003
Ending Page	6859
Page Count	8
Starting Page	6852
File Format	PDF
ISSN	00219193
e-ISSN	10985530
Journal	Journal of Bacteriology
Issue Number	23
Volume Number	185
Language	English
Publisher	American Society for Microbiology
Publisher Date	2003-12-01
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Molecular Biology Microbiology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Molecular Biology Microbiology

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Collaborative Regulation of Escherichia coli Glutamate-Dependent Acid Resistance by Two AraC-Like Regulators, GadX and GadW (YhiW)

Genes of the GadX-GadW Regulon in Escherichia coli

Mechanisms of Transcription Activation Exerted by GadX and GadW at the gadA and gadBC Gene Promoters of the Glutamate-Based Acid Resistance System in Escherichia coli ▿

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pH-Dependent Modulation of Cyclic AMP Levels and GadW-Dependent Repression of RpoS Affect Synthesis of the GadX Regulator and Escherichia coli Acid Resistance

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