DivIVA controls the dynamics of septum splitting and cell elongation in Streptococcus pneumoniae

Abstract

Bacterial shape and division rely on the dynamics of cell wall assembly, which involves regulated synthesis and cleavage of the peptidoglycan. In ovococci, these processes are coordinated in an annular mid-cell region with nanometric dimensions. More precisely, the cross-wall that is synthesized by the divisome is split to generate lateral wall, whose expansion is insured by insertion of so-called peripheral peptidoglycan by the elongasome. Septum cleavage and peripheral peptidoglycan synthesis are thus crucial remodeling events for ovococcal cell division and elongation. The structural DivIVA protein has long been known as a major regulator of these processes but its mode of action remains unknown. Here, we integrate click chemistry-based peptidoglycan labeling, direct stochastic optical reconstruction microscopy and in silico modeling, as well as epifluorescence and stimulated emission depletion microscopy to investigate the role of DivIVA in Streptococcus pneumoniae cell morphogenesis. Our work reveals two distinct phases of peptidoglycan remodeling along the cell cycle, that are differentially controlled by DivIVA. In particular, we show that DivIVA ensures homogeneous septum cleavage and peripheral peptidoglycan synthesis around the division site, and their maintenance throughout the cell cycle. Our data additionally suggest that DivIVA impacts the contribution of the elongasome and class A PBPs to cell elongation. We also report the position of DivIVA on either side of the septum, consistent with its known affinity for negatively curved membranes. Finally, we take the opportunity provided by these new observations to propose hypotheses for the mechanism of action of this key morphogenetic protein. IO_SCPLOWMPORTANCEC_SCPLOWThis study sheds light on fundamental processes governing bacterial cell growth and division, using integrated click chemistry, advanced microscopy and computational modeling approaches. More precisely, it addresses mechanisms involved in the regulation of cell wall synthesis and remodeling in Streptococcus pneumoniae. This bacterium belongs to the morphological group of ovococci, which includes many human pathogens, such as streptococci and enterococci. In this study, we have dissected the function of DivIVA, which is a structural protein involved in cell division, cell morphogenesis and chromosome partitioning in Gram-positive bacteria. This work unveils the role of DivIVA in the orchestration of cell division and elongation along the pneumococcal cell cycle. It not only helps understanding how ovoid bacteria proliferate, but also offers an opportunity to consider how DivIVA might serve as a scaffold and sensor for particular membrane regions, and thus be involved in various processes associated with the cell cycle.