1887

Abstract

Acid resistance is an important feature of both pathogenic and non-pathogenic . 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 and ) and a putative glutamate:γ-amino butyric acid antiporter (encoded by ). 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 and mRNA levels. Fusions between and the and 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 σ and is repressed by the cAMP receptor protein (CRP). In contrast, σ has only a minor role in transcription in cells grown in minimal media. Deletions of the regulatory region upstream of provided evidence that a 20 bp conserved region located 50 bp from the transcriptional start of both operons is required for expression.

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/content/journal/micro/10.1099/00221287-147-3-709
2001-03-01
2019-10-14
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