MecA dampens transitions to spore, biofilm exopolysaccharide and competence expression by two different mechanisms.

The adapter protein MecA targets the transcription factor ComK for degradation by the ClpC/ClpP proteolytic complex, thereby negatively regulating competence in Bacillus subtilis. Here we show that MecA also decreases the frequency of transitions to the sporulation pathway as well as the expression of eps, which encodes synthesis of the biofilm matrix exopolysaccharide. We present genetic and biophysical evidence that MecA downregulates eps expression and spore formation by directly interacting with Spo0A. MecA does not target Spo0A for degradation, and apparently does not prevent the phosphorylation of Spo0A. We propose that it inhibits the transcriptional activity of Spo0A∼P by direct binding. Thus, in its interaction with Spo0A, MecA differs from its role in the regulation of competence where it targets ComK for degradation. MecA acts as a general buffering protein for development, acting by two distinct mechanisms to regulate inappropriate transitions to energy-intensive pathways.