Localized Peptidoglycan Biosynthesis in Chlamydia trachomatis Conforms to the Polarized Division and Cell Size Reduction Developmental Models

Abstract

Cell size regulation in bacteria is a function of two basic cellular processes: the expansion of the cell envelope and its constriction at spatially defined points at what will eventually become the division plane. In most bacterial species, both cell wall expansion and restriction are dependent on peptidoglycan (PG), a structural polymer comprised of sugars and amino acids that imparts strength and rigidity to bacterial membranes. Pathogenic Chlamydia species are unique in that their cell walls contain very little PG, which is restricted almost entirely to the apparent division plane of the microbe’s replicative forms. Very little is known about the degree to which PG affects the size and shape of C. trachomatis during its division process, and recent studies suggest the process is initiated via a polarized mechanism. We conducted an imaging study to ascertain the dimensions, orientation, and relative density of chlamydial PG throughout the organism’s developmental cycle. Our analysis indicates that PG in replicating C. trachomatis can be associated with four, broad structural forms; polar/septal disks, small/thick rings, large rings, and small/thin rings. We found that PG density appeared to be highest in septal disks and small/thick rings, indicating that these structures likely have high PG synthesis to degradation ratios. We also discovered that as C. trachomatis progresses through its developmental cycle PG structures, on average, decrease in total volume, indicating that the average cell volume of chlamydial RBs likely decreases over time. When cells infected with C. trachomatis are treated with inhibitors of critical components of the microbe’s two distinct PG synthases, we observed drastic differences in the ratio of PG synthesis to degradation, as well as the volume and shape of PG-containing structures. Overall, our results suggest that C. trachomatis PG synthases differentially regulate the expansion and contraction of the PG ring during both the expansion and constriction of the microbe’s cell membrane during cell growth and division, respectively.

An NlpC/P60 protein catalyzes a key step in peptidoglycan recycling at the intersection of energy recovery, cell division and immune evasion in the intracellular pathogen Chlamydia trachomatis

“…The unusual process of cell division in Chlamydiaceae is initiated by a budding mechanism similar to that in FtsZ lacking Planctomycetes [ 22 ]. The asymmetric cell poles then mature into two approximately equally-sized daughter cells separated by an MreB-controlled septum containing a transient PGN ring which is remodeled during constriction and degraded afterwards [ 5 , 23 ].…”

The MraY Inhibitor Muraymycin D2 and Its Derivatives Induce Enlarged Cells in Obligate Intracellular Chlamydia and Wolbachia and Break the Persistence Phenotype in Chlamydia

“…Compared with MRY D2 inhibiting the formation of lipid I, PEN G acts downstream of MraY in the chlamydial PGN synthesis pathway (Figures 7 and 8). It binds to the transpeptidases PBP2 and PBP3 and the D,D-carboxypeptidase PBP6 [39,64], thereby inhibiting synthesis of cross-linked PGN and blocking cell division [36][37][38]. Although PEN G and MRY D2 both halt chlamydial cell division, different processes are likely to be involved at a cellular level in the bacteria.…”

“…PEN binds to penicillinbinding proteins (PBPs) and thereby interferes with the transpeptidation and remodeling of PGN, which is usually bactericidal in many bacteria via not fully understood cellular downstream effects. PEN acts bacteriostatically in Chlamydia and induces a reversible state of persistence by blocking cell division, which leads to the formation of enlarged ABs that persist within the host cell [14,[37][38][39]. Wolbachia, on the other hand, are unaffected by PEN treatment [40] but are susceptible to fosfomycin [32], which lacks activity against Chlamydia due to intrinsic resistance [41].…”

Aberrant Bodies: An Alternative Metabolic Homeostasis Allowing Survivability?

“…The septal disk expands to form a ring, which then constricts to finalize the division process. In C. trachomatis , penicillin binding protein 2 (PBP2) and PBP3 are two regulators which are independently responsible for the peptidoglycan ring expansion and constriction, respectively [ 83 , 84 ]. It has been observed that the volume and thickness of the ring decreases with the number of divisions that have occurred, resulting in smaller bacterial progeny size as infection time progresses.…”

“…Alternatively, peptidoglycan ring constriction can be inhibited by PBP3 inhibitors such as piperacillin. Broad spectrum β-lactamase inhibitors, like penicillin G, are able to target both PBP2 and PBP3 [ 83 , 84 ]. It is likely that a similar mechanism is present in the other members of the Chlamydiae phylum, as they all have homologs of PBP2 and PBP3 [ 73 ].…”