Regulatory roles of the LysR-type transcriptional regulator GltC in metabolism, stress tolerance, and virulence of Listeria monocytogenes

Abstract

ABSTRACT Listeria monocytogenes is a gram-positive facultative intracellular bacterium that causes listeriosis in humans and animals. Survival in diverse environments and host-associated niches requires coordinated regulation of metabolism, stress responses, and virulence. The LysR-type transcriptional regulator GltC is predicted to regulate glutamate metabolism, yet its broader contribution to metabolic regulation and pathogenicity in L. monocytogenes remains unclear. Here, we explored the role of GltC in nitrogen utilization, central carbon metabolism, stress tolerance, and virulence. Deletion of gltC had no detectable effect on growth under nutrient-rich, nitrogen-defined conditions or at acidic and alkaline pH, indicating that GltC is not required for basal fitness. Instead, loss of gltC triggered extensive transcriptional remodeling of nitrogen assimilation pathways, including altered expression of genes involved in glutamate synthesis, ammonium transport, and ethanolamine utilization, as well as condition-dependent changes in tricarboxylic acid cycle-associated genes. The ΔgltC mutant exhibited enhanced tolerance to oxidative stress, with improved growth and survival during hydrogen peroxide challenge and increased expression of oxidative stress defense and DNA repair genes. Deletion of gltC led to broad upregulation of the PrfA virulence regulon and a modest increase in hemolytic activity. The ΔgltC strain displayed significantly higher bacterial burdens in the spleen and liver in a murine infection model. Collectively, these results suggest that GltC contributes to the coordination of nitrogen metabolism and oxidative stress adaptation, while influencing bacterial fitness during systemic infection. IMPORTANCE Pathogenic bacteria must constantly balance nutrient acquisition, metabolic activity, and virulence to persist in changing environments. Listeria monocytogenes causes severe foodborne disease and must adapt to changing nutrient and stress conditions during infection. Understanding how metabolism influences virulence is critical for identifying new strategies to limit bacterial survival in the host. This study shows that GltC contributes to the coordination of nitrogen metabolism, oxidative stress adaptation, and bacterial fitness during L. monocytogenes infection. Although GltC is not required for basic growth, its loss alters nitrogen metabolic pathways, enhances oxidative stress tolerance, and is associated with increased bacterial burdens during murine infection. These findings provide new insights into how metabolic regulation influences bacterial adaptation and fitness during host infection. Pathogenic bacteria must constantly balance nutrient acquisition, metabolic activity, and virulence to persist in changing environments. Listeria monocytogenes causes severe foodborne disease and must adapt to changing nutrient and stress conditions during infection. Understanding how metabolism influences virulence is critical for identifying new strategies to limit bacterial survival in the host. This study shows that GltC contributes to the coordination of nitrogen metabolism, oxidative stress adaptation, and bacterial fitness during L. monocytogenes infection. Although GltC is not required for basic growth, its loss alters nitrogen metabolic pathways, enhances oxidative stress tolerance, and is associated with increased bacterial burdens during murine infection. These findings provide new insights into how metabolic regulation influences bacterial adaptation and fitness during host infection.