MntR Mediates LiaSR-Regulated gadT2/gadD2 Expression and Acid Resistance in Listeria monocytogenes 10403S

Listeria monocytogenes is a foodborne pathogen that can survive acid stress. The glutamate decarboxylase (GAD) system is an important system that helps L. monocytogenes to survive in acidic environments. A previous report showed that the two-component system LiaSR negatively regulates the gadT2/gadD2 cluster and is involved in acid resistance in L. monocytogenes 10403S. This study aimed to clarify how LiaSR regulates gadT2/gadD2. We found that the expression of gadT2/gadD2 was positively regulated by the transcription factor MntR. Survival assays showed that mntR deletion significantly reduced the survival rate of L. monocytogenes under different acidic conditions. Moreover, the expression level of MntR was negatively regulated by the two-component system LiaSR under different pH conditions as shown by the reporter assay. The electrophoretic mobility shift assay (EMSA) showed that MntR directly bound the gadT2/gadD2 promoter and LiaR directly bound the mntR promoter. Finally, the liaSR/mntR double deletion significantly downregulated the expression of gadT2/gadD2 under acidic conditions and weakens the acid resistance of L. monocytogenes, indicating that MntR plays an important regulatory role in the LiaSR-MntR-gadT2/gadD2 regulatory axis. In summary, we demonstrated that the two-component system LiaSR negatively regulates MntR to inhibit the expression of gadT2/gadD2 cluster to regulate acid resistance of L. monocytogenes.