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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

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dc.contributor.author Karatzas, Kimon-Andreas G.
dc.contributor.author Brennan, Orla
dc.contributor.author Heavin, Sinead
dc.contributor.author Morrissey, John J.
dc.date.accessioned 2012-03-05T13:45:41Z
dc.date.available 2012-03-05T13:45:41Z
dc.date.issued 2010-06
dc.identifier.citation Karatzas KA, Brennan O, Heavin S, Morrissey J, O'Byrne CP. (2010) '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'. Appl Environ Microbiol, 76 (11):3529-3537. en_US
dc.identifier.issn 0099-2240
dc.identifier.uri http://hdl.handle.net/10379/2592
dc.description.abstract 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. en_US
dc.description.sponsorship Department of Agriculture, Fisheries and Food (grant no. 06/RD/C/459) en_US
dc.format application/pdf en_US
dc.language.iso en en_US
dc.publisher American Society for Microbiology en_US
dc.relation.ispartof Appl Environ Microbiol. en
dc.subject Acid resistance en_US
dc.subject Glutatmate decarboxylase en_US
dc.subject Escherichia-coli en_US
dc.subject Identification en_US
dc.subject Components en_US
dc.subject Bacteria en_US
dc.subject Chloride en_US
dc.subject Regulon en_US
dc.subject Stress en_US
dc.subject System en_US
dc.title 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 en_US
dc.type Article en_US
dc.date.updated 2012-02-15T16:24:19Z
dc.identifier.doi DOI 10.1128/AEM.03063-09
dc.local.publishedsource http://dx.doi.org/10.1128/AEM.03063-09 en_US
dc.description.peer-reviewed peer-reviewed
dc.contributor.funder |~|
dc.internal.rssid 1143374
dc.local.contact Conor O'Byrne, Dept. Of Microbiology, Arts/Science Building, Nui Galway. 3957 Email: conor.obyrne@nuigalway.ie
dc.local.copyrightchecked No
dc.local.version PUBLISHED

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