SEDS-bPBP pairs direct lateral and septal peptidoglycan synthesis in Staphylococcus aureus

Peptidoglycan (PGN) is the major component of the bacterial cell wall, a structure that is essential for the physical integrity and shape of the cell. Bacteria maintain cell shape by directing PGN incorporation to distinct regions of the cell, namely, through the localization of late-stage PGN synthesis proteins. These include two key protein families, SEDS transglycosylases and bPBP transpeptidases, proposed to function in cognate pairs. Rod-shaped bacteria have two SEDS-bPBP pairs, involved in elongation and division. Here, we elucidate why coccoid bacteria, such as Staphylococcus aureus, also possess two SEDS-bPBP pairs. We determined that S. aureus RodA-PBP3 and FtsW-PBP1 probably constitute cognate pairs of interacting proteins. A lack of RodA-PBP3 resulted in more spherical cells due to deficient sidewall PGN synthesis, whereas depletion of FtsW-PBP1 arrested normal septal PGN incorporation. Although PBP1 is an essential protein, a mutant lacking PBP1 transpeptidase activity is viable, showing that this protein has a second function. We propose that the FtsW-PBP1 pair has a role in stabilizing the divisome at midcell. In the absence of these proteins, the divisome appears as multiple rings or arcs that drive lateral PGN incorporation, leading to cell elongation. We conclude that RodA-PBP3 and FtsW-PBP1 mediate sidewall and septal PGN incorporation, respectively, and that their activity must be balanced to maintain coccoid morphology.