Document Detail

Intracellular accumulation of high levels of gamma-aminobutyrate by Listeria monocytogenes 10403S in response to low pH: uncoupling of gamma-aminobutyrate synthesis from efflux in a chemically defined medium.
MedLine Citation:
PMID:  20400565     Owner:  NLM     Status:  MEDLINE    
It is well established that the glutamate decarboxylase (GAD) system is central to the survival of Listeria monocytogenes at low pH, both in acidic foods and within the mammalian stomach. The accepted model proposes that under acidic conditions extracellular glutamate is transported into the cell in exchange for an intracellular gamma-aminobutyrate (GABA(i)). The glutamate is then decarboxylated to GABA(i), a reaction that consumes a proton, thereby helping to prevent acidification of the cytoplasm. In this study, we show that glutamate supplementation had no influence on either growth rate at pH 5.0 or survival at pH 2.5 when L. monocytogenes 10403S was grown in a chemically defined medium (DM). In response to acidification, cells grown in DM failed to efflux GABA, even when glutamate was added to the medium. In contrast, in brain heart infusion (BHI), the same strain produced significant extracellular GABA (GABA(e)) in response to acidification. In addition, high levels of GABA(i) (>80 mM) were found in the cytoplasm in response to low pH in both growth media. Medium-swap and medium-mixing experiments revealed that the GABA efflux apparatus was nonfunctional in DM, even when glutamate was present. It was also found that the GadT2D2 antiporter/decarboxylase system was transcribed poorly in DM-grown cultures while overexpression of gadD1T1 and gadD3 occurred in response to pH 3.5. Interestingly, BHI-grown cells did not respond with upregulation of any of the GAD system genes when challenged at pH 3.5. The accumulation of GABA(i) in cells grown in DM in the absence of extracellular glutamate indicates that intracellular glutamate is the source of the GABA(i). These results demonstrate that GABA production can be uncoupled from GABA efflux, a finding that alters the way we should view the operation of bacterial GAD systems.
Kimon-Andreas G Karatzas; Orla Brennan; Sinéad Heavin; John Morrissey; Conor P O'Byrne
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2010-04-16
Journal Detail:
Title:  Applied and environmental microbiology     Volume:  76     ISSN:  1098-5336     ISO Abbreviation:  Appl. Environ. Microbiol.     Publication Date:  2010 Jun 
Date Detail:
Created Date:  2010-05-20     Completed Date:  2010-09-28     Revised Date:  2013-05-29    
Medline Journal Info:
Nlm Unique ID:  7605801     Medline TA:  Appl Environ Microbiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  3529-37     Citation Subset:  IM    
Bacterial Stress Response Group, Microbiology, School of Natural Sciences, National University of Ireland-Galway, Ireland.
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MeSH Terms
Culture Media / chemistry*
Cytosol / chemistry*
Glutamic Acid / metabolism
Hydrogen-Ion Concentration
Listeria monocytogenes / growth & development,  metabolism,  physiology*
Microbial Viability
Stress, Physiological*
gamma-Aminobutyric Acid / metabolism*
Reg. No./Substance:
0/Culture Media; 56-12-2/gamma-Aminobutyric Acid; 56-86-0/Glutamic Acid

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