Role of FruR transcriptional regulator in virulence of Listeria monocytogenes and identification of its regulon

Abstract

Listeria monocytogenesis a ubiquitous opportunistic foodborne pathogen capable of survival in various adverse environmental conditions. Pathogenesis ofL.monocytogenesis tightly controlled by a complex regulatory network of transcriptional regulators that are necessary for survival and adaptations to harsh environmental conditions both inside and outside host cells. Among these regulatory pathways are members of the DeoR-family transcriptional regulators that are known to play a regulatory role in sugar metabolism. In this study, we deciphered the role of FruR, a DeoR family protein, which is a fructose operon transcriptional repressor protein, inL.monocytogenespathogenesis and growth. Following intravenous (IV) inoculation in mice, a mutant strain with deletion offruRexhibited a significant reduction in bacterial burden in liver and spleen tissues compared to the parent strain. Further, the ΔfruRstrain had a defect in cell-to-cell spread in L2 fibroblast monolayers. Constitutive activation of PrfA, a pleiotropic activator ofL.monocytogenesvirulence factors, did not restore virulence to the ΔfruRstrain, suggesting that the attenuation was not a result of impaired PrfA activation. Transcriptome analysis revealed that FruR functions as a positive regulator for genes encoding enzymes involved in the pentose phosphate pathway (PPP) and as a repressor for genes encoding enzymes in the glycolysis pathway. These results suggested that FruR may function to facilitate NADPH regeneration, which is necessary for full protection from oxidative stress. Interestingly, deletion offruRincreased sensitivity ofL.monocytogenesto H2O2, confirming a role for FruR in survival ofL.monocytogenesduring oxidative stress. Using anti-mouse neutrophil/monocyte monoclonal antibody RB6-8C5 (RB6) in anin vivoinfection model, we found that FruR has a specific function in protectingL.monocytogenesfrom neutrophil/monocyte-mediated killing. Overall, this work clarifies the role of FruR in controllingL.monocytogenescarbon flow between glycolysis and PPP for NADPH homeostasis, which provides a new mechanism allowing metabolic adaptation ofL.monocytogenesto oxidative stress.