Identification in Listeria monocytogenes of MecA, a homologue of the Bacillus subtilis competence regulatory protein

We identified in Listeria monocytogenes a gene encoding a protein homologous to MecA, a regulatory protein acting with ClpC and ComK in the competence pathway of Bacillus subtilis. In L. monocytogenes, MecA is involved, along with ClpC and ClpP, in the downregulation of a 64-kDa secreted protein. In B. subtilis, the MecA protein of L. monocytogenes behaves as a regulatory protein, controlling the transcription of comK and comG. Complete or disrupted ComK homologues mere also found in L. monocytogenes. However, we failed to detect competence in various strains of L. monocytogenes, including those with intact ComK. Our results suggest that the functions of MecA in the saprophytes L. monocytogenes and B. subtilis have presumably diverged in response to their respective ecological niches.