Roles of RodZ and Class A PBP1b in the Assembly and Regulation of the Peripheral Peptidoglycan Elongasome in Ovoid-Shaped Cells ofStreptococcus pneumoniaeD39

SUMMARY RodZ of rod-shaped bacteria functions to link MreB filaments to the Rod peptidoglycan (PG) synthase complex that moves circumferentially perpendicular to the long cell axis, creating hoop-like sidewall PG. Ovoid-shaped bacteria, such as Streptococcus pneumoniae (pneumococcus; Spn ) that lack MreB, use a different modality for peripheral PG elongation that emanates from the midcell of dividing cells. Yet, S. pneumoniae encodes a RodZ homolog similar to RodZ in rod-shaped bacteria. We show here that the helix-turn-helix and transmembrane domains of RodZ( Spn ) are essential for growth at 37°C. Δ rodZ mutations are suppressed by Δ pbp1a , mpgA (Y488D), and Δ khpA mutations that suppress Δ mreC , but not Δ cozE . Consistent with a role in PG elongation, RodZ( Spn ) co-localizes with MreC and aPBP1a throughout the cell cycle and forms complexes and interacts with PG elongasome proteins and regulators. Depletion of RodZ( Spn ) results in aberrantly shaped, non-growing cells and mislocalization of elongasome proteins MreC, PBP2b, and RodA. Moreover, Tn-seq reveals that RodZ( Spn ), but not MreCD( Spn ), displays a specific synthetic-viable genetic relationship with aPBP1b, whose function is unknown. We conclude that RodZ( Spn ) acts as a scaffolding protein required for elongasome assembly and function and that aPBP1b, like aPBP1a, plays a role in elongasome regulation and possibly peripheral PG synthesis. Graphical Summary