Document Detail

Characterization of the intracellular glutamate decarboxylase system: analysis of its function, transcription, and role in the acid resistance of various strains of Listeria monocytogenes.
MedLine Citation:
PMID:  22407692     Owner:  NLM     Status:  MEDLINE    
The glutamate decarboxylase (GAD) system is important for the acid resistance of Listeria monocytogenes. We previously showed that under acidic conditions, glutamate (Glt)/γ-aminobutyrate (GABA) antiport is impaired in minimal media but not in rich ones, like brain heart infusion. Here we demonstrate that this behavior is more complex and it is subject to strain and medium variation. Despite the impaired Glt/GABA antiport, cells accumulate intracellular GABA (GABA(i)) as a standard response against acid in any medium, and this occurs in all strains tested. Since these systems can occur independently of one another, we refer to them as the extracellular (GAD(e)) and intracellular (GAD(i)) systems. We show here that GAD(i) contributes to acid resistance since in a ΔgadD1D2 mutant, reduced GABA(i) accumulation coincided with a 3.2-log-unit reduction in survival at pH 3.0 compared to that of wild-type strain LO28. Among 20 different strains, the GAD(i) system was found to remove 23.11% ± 18.87% of the protons removed by the overall GAD system. Furthermore, the GAD(i) system is activated at milder pH values (4.5 to 5.0) than the GAD(e) system (pH 4.0 to 4.5), suggesting that GAD(i) is the more responsive of the two and the first line of defense against acid. Through functional genomics, we found a major role for GadD2 in the function of GAD(i), while that of GadD1 was minor. Furthermore, the transcription of the gad genes in three common reference strains (10403S, LO28, and EGD-e) during an acid challenge correlated well with their relative acid sensitivity. No transcriptional upregulation of the gadT2D2 operon, which is the most important component of the GAD system, was observed, while gadD3 transcription was the highest among all gad genes in all strains. In this study, we present a revised model for the function of the GAD system and highlight the important role of GAD(i) in the acid resistance of L. monocytogenes.
Kimon-Andreas G Karatzas; Laura Suur; Conor P O'Byrne
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2012-03-09
Journal Detail:
Title:  Applied and environmental microbiology     Volume:  78     ISSN:  1098-5336     ISO Abbreviation:  Appl. Environ. Microbiol.     Publication Date:  2012 May 
Date Detail:
Created Date:  2012-04-26     Completed Date:  2012-08-15     Revised Date:  2013-06-26    
Medline Journal Info:
Nlm Unique ID:  7605801     Medline TA:  Appl Environ Microbiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  3571-9     Citation Subset:  IM    
Bacterial Stress Response Group, Microbiology, School of Natural Sciences, National University of Ireland, Galway, Galway, Ireland.
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MeSH Terms
Acids / metabolism*,  toxicity
Culture Media / chemistry
Drug Resistance, Bacterial
Gene Deletion
Gene Expression Regulation, Bacterial*
Glutamate Decarboxylase / genetics*,  metabolism*
Listeria monocytogenes / enzymology*,  genetics*
Microbial Viability / drug effects
Stress, Physiological*
Transcription, Genetic
gamma-Aminobutyric Acid / metabolism
Reg. No./Substance:
0/Acids; 0/Culture Media; 56-12-2/gamma-Aminobutyric Acid; EC Decarboxylase

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