Transcriptional and post‐transcriptional regulation of the GmaR antirepressor governs temperature‐dependent control of flagellar motility in Listeria monocytogenes

Abstract

Flagellar motility in Listeria monocytogenes (Lm) is restricted to temperatures below 37°C due to the opposing activities of the MogR transcriptional repressor and the GmaR antirepressor. Previous studies have suggested that both the DegU response regulator and MogR regulate expression of GmaR. In this report, we further define the role of DegU for GmaR production and flagellar motility. We demonstrate that deletion of the receiver domain of DegU has no effect on flagellar motility in Lm. Using transcriptional reporter fusions, we determined that gmaR is cotranscribed within an operon initiating with fliN. Furthermore, the fliN-gmaR promoter (p_fliN-gmaR) is transcriptionally activated by DegU and is also MogR-repressed. DNA affinity purification, gel mobility shift and footprinting analyses revealed that both DegU and MogR directly bind fliN-gmaR promoter region DNA and that the binding sites do not overlap. Quantitative analysis of gmaR transcripts in ΔmogR bacteria indicated that transcriptional activation of p_fliN-gmaR by DegU is not inherently temperature-dependent. However, GmaR protein was not detectable at 37°C in ΔmogR bacteria, indicating that a temperature-dependent, post-transcriptional mechanism limits GmaR production to temperatures below 37°C. Our findings reveal that flagellar motility in Lm is governed by both temperature-dependent transcriptional and post-transcriptional regulation of the GmaR antirepressor.