The cell envelope stress response mediated by the LiaFSRLm three-component system of Listeria monocytogenes is controlled via the phosphatase activity of the bifunctional histidine kinase LiaSLm.

Most members of the phylum Firmicutes harbour a two-component system (TCS), LiaSR, which is involved in the response to cell envelope stress elicited most notably by inhibitors of the lipid II cycle. In all LiaSR systems studied in detail, LiaSR-mediated signal transduction has been shown to be negatively controlled by a membrane protein, LiaF, encoded upstream of liaSR. In this study we have analysed the LiaSR orthologue of Listeria monocytogenes (LiaSR(Lm)). Whole-genome transcriptional profiling indicated that activation of LiaSR(Lm) results in a remodelling of the cell envelope via the massive upregulation of membrane-associated and extracytoplasmic proteins in the presence of inducing stimuli. As shown for other LiaSR TCSs, LiaSR(Lm) is activated by cell wall-active antibiotics. We demonstrate that the level of phosphorylated LiaR(Lm), which is required for the induction of the LiaSR(Lm) regulon, is controlled by the interplay between the histidine kinase and phosphatase activities of the bifunctional sensor protein LiaS(Lm). Our data suggest that the phosphatase activity of LiaS(Lm) is stimulated by LiaF(Lm) in the absence of cell envelope stress.

Response regulator DegU of Listeria monocytogenes controls temperature-responsive flagellar gene expression in its unphosphorylated state.

We demonstrate that in Listeria monocytogenes, temperature-responsive transcriptional control of flagellar genes does not rely on the phosphorylation of the conserved phosphorylation site (D55) in the receiver domain of response regulator DegU. Furthermore, proper control of DegU-regulated genes involved in ethanol tolerance and virulence is independent of receiver phosphorylation.