Transient inhibition of cell division in competent pneumococcal cells results from deceleration of the septal peptidoglycan complex

Bacterial cells are known to produce inhibitors of cell division in response to stress responses and developmental programs. Knowledge of the underlying molecular mechanisms remains however largely limited. In this study, we investigated the mechanism of transient cell division inhibition observed during the development of competence for transformation in the human pathogen Streptococcus pneumoniae. In this species, ComM, a membrane protein specifically produced during competence, transiently inhibits cell division to preserve genomic integrity during transformation. We show that ComM reduces specifically the dynamics of the septal peptidoglycan synthetic complex FtsW:PBP2x. We also present evidence that ComM interacts with the peptidoglycan precursor synthetic enzyme MurA, and show that overproduction of MurA suppresses FtsW:PBP2x deceleration along the cell division delay in competent cells. Collectively, our data support a model in which ComM interferes with MurA activity to reduce septal peptidoglycan synthesis during competence in S. pneumoniae.