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Applied and Environmental Microbiology, July 2009, p. 4231-4239, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.00051-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

New Insights into {gamma}-Aminobutyric Acid Catabolism: Evidence for {gamma}-Hydroxybutyric Acid and Polyhydroxybutyrate Synthesis in Saccharomyces cerevisiae{triangledown}

Benoît Bach,1,{dagger} Emmanuelle Meudec,1 Jean-Paul Lepoutre,1 Tristan Rossignol,1,{ddagger} Bruno Blondin,2 Sylvie Dequin,1 and Carole Camarasa1*

UMR1083 Sciences pour l'Oenologie, INRA,1 SupAgro Montpellier, F-34060 Montpellier, France2

Received 9 January 2009/ Accepted 22 April 2009

The {gamma}-aminobutyrate (GABA) shunt, an alternative route for the conversion of {alpha}-ketoglutarate to succinate, involves the glutamate decarboxylase Gad1p, the GABA transaminase Uga1p and the succinate semialdehyde dehydrogenase Uga2p. This pathway has been extensively described in plants and animals, but its function in yeast remains unclear. We show that the flux through Gad1p is insignificant during fermentation in rich sugar-containing medium, excluding a role for this pathway in redox homeostasis under anaerobic conditions or sugar stress. However, we found that up to 4 g of exogenous GABA/liter was efficiently consumed by yeast. We studied the fate of this consumed GABA. Most was converted into succinate, with a reaction yield of 0.7 mol/mol. We also showed that a large proportion of GABA was stored within cells, indicating a possible role for this molecule in stress tolerance mechanisms or nitrogen storage. Furthermore, based on enzymatic and metabolic evidence, we identified an alternative route for GABA catabolism, involving the reduction of succinate-semialdehyde into {gamma}-hydroxybutyric acid and the polymerization of {gamma}-hydroxybutyric acid to form poly-(3-hydroxybutyric acid-co-4-hydroxybutyric acid). This study provides the first demonstration of a native route for the formation of this polymer in yeast. Our findings shed new light on the GABA pathway and open up new opportunities for industrial applications.

* Corresponding author. Mailing address: UMR1083 Sciences pour l'Oenologie, INRA, 2 Place Viala, F-34060 Montpellier, France. Phone: (33) 4 99 61 23 36. Fax: (33) 4 99 61 28 57. E-mail: camarasa{at}supagro.inra.fr

{triangledown} Published ahead of print on 1 May 2009.

{dagger} Present address: Inter-Rhône, F-84100 Orange, France.

{ddagger} Present address: USC2019 INRA-Institut Pasteur, F-75724 Paris, France.

Applied and Environmental Microbiology, July 2009, p. 4231-4239, Vol. 75, No. 13
0099-2240/09/$08.00+0     doi:10.1128/AEM.00051-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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