Characterization of ylbF, a new gene involved in competence development and sporulation in Bacillus subtilis

We used mini Tn10 transposition to generate a library of Bacillus subtilis insertion mutants, with the goal of identifying and characterizing new competence genes. Two new regulatory genes were identified in our screen: ypuN (also known as rsiX, the anti-sigmaX factor) and ylbF. The disruption of ylbF leads to a dramatic decrease in the expression of comK, encoding the competence transcription factor. Our data show that ylbF positively controls ComK at a post-transcriptional level. It has been reported previously that ComK is degraded in vivo and in vitro by a multimeric protein complex composed of ClpP, ClpC and MecA. This proteolysis is inhibited by the ComS peptide. We show that both the overexpression of comS and the inactivation of mecA individually suffice to bypass the competence phenotype of the ylbF mutation. This mutation does not seem to alter the cellular concentrations of MecA or ClpP, and we propose a role for YlbF in modulating the translation, stability or activity of ComS. In addition to its role in competence, ylbF also appears to regulate sporulation by acting before stage II.