Modification of cell wall polysaccharide guides cell division in Streptococcus mutans

In ovoid-shaped Gram-positive bacteria, MapZ guides FtsZ-ring positioning at cell equators. The cell wall of the ovococcus Streptococcus mutans contains peptidoglycan decorated with Serotype c Carbohydrates (SCCs). In this study, we identify the major cell separation autolysin AtlA as an SCC binding protein. AtlA binding to SCC is attenuated by the glycerol phosphate (GroP) modification. Using fluorescently-labeled AtlA constructs, we mapped SCC distribution on the streptococcal surface revealing enrichment of GroP-deficient immature SCCs at the cell poles and equators. The immature SCCs co-localize with MapZ at the equatorial rings throughout the cell cycle. In GroP-deficient mutants, AtlA is mislocalized resulting in dysregulated cellular autolysis. These mutants display morphological abnormalities associated with MapZ mislocalization leading to FtsZ-ring misplacement. Altogether, our data support a model in which maturation of a cell wall polysaccharide provides the molecular cues for the recruitment of cell division machinery, ensuring proper daughter cell separation and FtsZ-ring positioning.