Abstract

Chlamydia trachomatis serovar L2 and Chlamydia muridarum, which do not express FtsZ, undergo polarized cell division. During division, peptidoglycan assembles at the pole of dividing Chlamydia trachomatis cells where daughter cell formation occurs, and peptidoglycan regulates at least two distinct steps in the polarized division of Chlamydia trachomatis and Chlamydia muridarum. Cells treated with inhibitors that prevent peptidoglycan synthesis or peptidoglycan crosslinking by penicillin-binding protein 2 (PBP2) are unable to initiate polarized division, while cells treated with inhibitors that prevent peptidoglycan crosslinking by penicillin-binding protein 3 (PBP3/FtsI) initiate polarized division, but the process arrests at an early stage of daughter cell growth. Consistent with their distinct roles in polarized division, peptidoglycan organization is different in cells treated with PBP2 and PBP3-specific inhibitors. Our analyses indicate that the sequential action of PBP2 and PBP3 drives changes in peptidoglycan organization that are essential for the polarized division of these obligate intracellular bacteria. Furthermore, the roles we have characterized for PBP2 and PBP3 in regulating specific steps in chlamydial cell division have not been described in other bacteria.

Highlights

  • Chlamydia trachomatis serovar L2 and Chlamydia muridarum, which do not express FtsZ, undergo polarized cell division

  • Our conclusion that C. trachomatis serovar L2 (Ct L2) undergoes polarized division was based on multiple criteria including a confocal microscopic analysis of fixed and stained cells, which revealed a characteristic distribution of the major outer membrane protein (MOMP), heat shock protein 60 (Hsp60), and DNA during the morphological changes that occur during division

  • In our initial studies we determined the percentage of the total reticulate body (RB) volume the nascent daughter cell and the progenitor mother cell comprise in dividing Ct L2 that were fixed and stained with MOMP and Hsp[60] antibodies at 10.5 and 11.5 h post-infection (Fig. 1)

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Summary

Introduction

Chlamydia trachomatis serovar L2 and Chlamydia muridarum, which do not express FtsZ, undergo polarized cell division. The vast majority of bacteria divide by a highly conserved process termed binary fission that requires the bacterial homologue of tubulin, FtsZ, we recently showed that Chlamydia trachomatis, which lacks FtsZ, replicates by a polarized cell division ­process[5] This novel polarized mechanism of division is characterized by: (1) the enlargement of a polarized RB, (2) the asymmetric expansion of the major outer membrane protein (MOMP)-enriched pole of the RB, resulting in the formation of a nascent budding daughter cell, and (3) the FtsZ-independent separation of the mother and daughter cell. Consistent with the distinct roles of PBP2 and PBP3 in chlamydial cell division, the organization of PG is very different in cells treated with PBP-specific inhibitors

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