Interplay of the serine/threonine-kinase StkP and the paralogs DivIVA and GpsB in pneumococcal cell elongation and division.

Aurore Fleurie,Jean-Pierre Lavergne,Nathalie Campo,Christophe Grangeasse,Caroline Cluzel,Jean-Pierre Claverys,Céline Freton,Chao Zhao,Anne-Marie Di Guilmi,Christophe Combet,Anne Galinier,Boris Macek,Boumediene Soufi,Erkin Kuru,Yves V Brun,Sébastien Guiral,Michael S Vannieuwenhze,Sylvie Manuse

doi:10.1371/journal.pgen.1004275

Abstract

Despite years of intensive research, much remains to be discovered to understand the regulatory networks coordinating bacterial cell growth and division. The mechanisms by which Streptococcus pneumoniae achieves its characteristic ellipsoid-cell shape remain largely unknown. In this study, we analyzed the interplay of the cell division paralogs DivIVA and GpsB with the ser/thr kinase StkP. We observed that the deletion of divIVA hindered cell elongation and resulted in cell shortening and rounding. By contrast, the absence of GpsB resulted in hampered cell division and triggered cell elongation. Remarkably, ΔgpsB elongated cells exhibited a helical FtsZ pattern instead of a Z-ring, accompanied by helical patterns for DivIVA and peptidoglycan synthesis. Strikingly, divIVA deletion suppressed the elongated phenotype of ΔgpsB cells. These data suggest that DivIVA promotes cell elongation and that GpsB counteracts it. Analysis of protein-protein interactions revealed that GpsB and DivIVA do not interact with FtsZ but with the cell division protein EzrA, which itself interacts with FtsZ. In addition, GpsB interacts directly with DivIVA. These results are consistent with DivIVA and GpsB acting as a molecular switch to orchestrate peripheral and septal PG synthesis and connecting them with the Z-ring via EzrA. The cellular co-localization of the transpeptidases PBP2x and PBP2b as well as the lipid-flippases FtsW and RodA in ΔgpsB cells further suggest the existence of a single large PG assembly complex. Finally, we show that GpsB is required for septal localization and kinase activity of StkP, and therefore for StkP-dependent phosphorylation of DivIVA. Altogether, we propose that the StkP/DivIVA/GpsB triad finely tunes the two modes of peptidoglycan (peripheral and septal) synthesis responsible for the pneumococcal ellipsoid cell shape.

Highlights

Bacterial cell growth and division are intimately linked
Bacterial genomics have revealed the presence of eukaryotic-type serine/threonine protein kinases (STKPs) in many bacteria
Considering that much remains to be discovered about the mechanisms by which the cell division machinery is assembled at the cell center and how the diversity of bacterial cell shapes is achieved and maintained, studying the role of STKPs represents a promising approach to decipher the inner workings of bacterial cell division

Summary

Introduction

Bacterial cell growth and division are intimately linked. Complex webs of proteins interacting with each other temporally and spatially control the cellular events leading to the production of two identical daughter cells [1,2,3]. Most of the proteins required for cell division and elongation have been characterized in rodshaped bacterial models like the Gram-negative bacteria Escherichia coli and Caulobacter crescentus or the Gram-positive bacterium Bacillus subtilis, and robust models depicting their division process are proposed. This knowledge has been beneficial for characterizing and understanding cell division of other bacteria. In the Gram-positive human pathogen Streptococcus pneumoniae (the pneumococcus), some conserved division proteins have been studied, but overall, little is known about the mechanisms governing cell division and those responsible for peptidoglycan (PG) synthesis, as well as how this species achieves its characteristic ellipsoid (rugby-ball like) shape [6,7,8,9,10].

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Conclusion