A one-track model for spatiotemporal coordination of Bacillus subtilis septal cell wall synthesis

Bacterial cell division requires synthesis of a septal peptidoglycan (sPG) wall across the middle of the cell. This is accomplished by the divisome synthesis complex in coordination with numerous other division proteins--such as the essential tubulin homolog FtsZ--but the molecular mechanism of its spatiotemporal regulation remains unclear. Here, we investigate the dynamics of sPG synthesis in the model Gram-positive bacterium Bacillus subtilis using live-cell single-molecule imaging of the divisome transpeptidase PBP2B. In contrast to previous models for division, we show that there is a single population of processively-moving PBP2B molecules whose motion is driven by peptidoglycan synthesis and is not associated with FtsZ treadmilling. However, although the motions of PBP2B and FtsZ are asynchronous, we demonstrate that processive PBP2B motion is partially dependent on FtsZ treadmilling. Additionally, we provide evidence that the divisome synthesis complex is multimeric. Our results support a new model for division in B. subtilis where a multimeric synthesis complex follows a single track dependent on sPG synthesis whose activity and dynamics are asynchronous with FtsZ treadmilling.