Methicillin treatment reveals that FtsZ phosphorylation influences the cell division of Streptococcus pneumoniae

Protein phosphorylation plays a crucial role in regulating cell division and morphogenesis in many bacteria. In Streptococcus pneumoniae, the serine/threonine kinase StkP orchestrates cell wall assembly and cell morphogenesis by phosphorylating several proteins involved in cell division. In this study, we provide evidence that FtsZ, a conserved tubulin-like protein that coordinates pneumococcal cell elongation and constriction, is phosphorylated in vivo by StkP at six phosphothreonine residues within its C-terminal linker (CTL). Mutational analysis reveals the structural role of the CTL in pneumococcal cell division and further shows that its phosphorylation status influences cell morphogenesis. Importantly, phosphomimetic FtsZ mutants rescue division blocks induced by sublethal concentrations of methicillin, which targets the essential septal cell wall synthase PBP2x. Additionally, we demonstrate that CTL phosphorylation affects FtsZ polymerization and filament bundling in vitro. It also accelerates FtsZ treadmilling dynamics and alters its interactome in vivo. Altogether, these findings support a model in which CTL phosphorylation fine-tunes FtsZ filament dynamics to sustain cell division under ß-lactam stress, representing a potential adaptive mechanism for antibiotic tolerance.