Escherichia coli acid resistance: cAMP receptor protein and a 20 bp cis-acting sequence control pH and stationary phase expression of the gadA and gadBC glutamate decarboxylase genes.
Acid resistance is an important feature of both pathogenic and non-pathogenic Escherichia coli. It enables survival in the acidic regions of mammalian gastrointestinal tracts and is largely responsible for the small number of bacteria required for infection/colonization. Three systems of acid resistance have been identified, the most efficient of which requires glutamic acid during pH 2 acid challenge. Three proteins associated with glutamate-dependent acid resistance have been identified. They are glutamate decarboxylase (encompassing two isozymes encoded by gadA and gadB) and a putative glutamate:gamma-amino butyric acid antiporter (encoded by gadC). The results confirm that the GadA and GadB proteins increase in response to stationary phase and low environmental pH. The levels of these proteins correspond to concomitant changes in gadA and gadBC mRNA levels. Fusions between lacZ and the gadA and gadBC operons indicate that this control occurs at the transcriptional level. Western blot, Northern blot and fusion analyses reveal that regulation of these genes is complex. Expression in rich media is restricted to stationary phase. However, in minimal media, acid pH alone can trigger induction in exponential or stationary phase cells. Despite this differential control, there is only one transcriptional start site for each gene. Expression in rich media is largely dependent on the alternate sigma factor sigma(S) and is repressed by the cAMP receptor protein (CRP). In contrast, sigma(S) has only a minor role in gad transcription in cells grown in minimal media. Deletions of the regulatory region upstream of gadA provided evidence that a 20 bp conserved region located 50 bp from the transcriptional start of both operons is required for expression.
Castanie-Cornet
Marie-Pierre
MP
Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, AL 36688, USA1.
Foster
John W
JW
Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, AL 36688, USA1.
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003470:Culture Media; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005968:Glutamate Decarboxylase / Q000235:genetics* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007763:Lac Operon / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D003470:Culture Media; D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; C121044:gadA protein, E coli; D005968:Glutamate Decarboxylase