MONOGAD - Elucidating Novel Roles and Mechanisms of the GAD System in Stress Resistance and Virulence of Listeria Monocytogenes

In previous work performed by Dr. Karatzas it has been demonstrated that the presence of glutamate does not confer any acid resistance to L. monocytogenes grown in DM. This is due to the absence of any GABA export in this medium even if glutamate is present. Furthermore, L. monocytogenes accumulates high levels of intracellular GABA when challenged with HCl in both rich media like BHI and DM. This accumulation of GABA intracellularly suggests that this response might protect cells under acidic conditions. <P>
We propose that the accumulation of intracellular but also of extracellular GABA buffers the acidic envinronment and therefore protects the cells. This hypothesis will be tested and the role of intracellular GABA will be assessed with experiments performed in a mutant missing all the decarboxylases. Furthermore, it is proposed to identify the source of intracellular GABA which is probably intracellular glutamate. In addition it will be investigated if any of the three decarboxylases is responsible specifically for the production of intracellular GABA. <P>
In previous work performed by Dr. Karatzas it has been demonstrated that previously unknown components in BHI activate the expression and the function of the GAD system in terms of GABA export. We propose to specifically identify these components and investigate if the regulation is at transcription level or if they are required for the activity of the antiporter-based GAD system.