A new metabolic cell wall labeling method reveals peptidoglycan in Chlamydia trachomatis

Peptidoglycan (PG), an essential structure in the cell walls of the vast majority of bacteria, is critical for division and maintaining cell shape and hydrostatic pressure(1). Bacteria comprising the Chlamydiales were thought to be one of the few exceptions. Chlamydia encodes genes for PG biosynthesis(2–7) and exhibits susceptibility to "anti-PG" antibiotics(8,9), yet attempts to detect PG in any chlamydial species have proven unsuccessful (the ‘chlamydial anomaly’(10)). We employed a novel approach to metabolically label chlamydial PG using D-amino acid dipeptide probes and click chemistry. Replicating Chlamydia trachomatis was labeled with the probes throughout its biphasic, developmental life cycle, and differential probe incorporation experiments conducted in the presence of ampicillin is consistent with the presence of chlamydial PG modifying enzymes. These findings culminate 50 years of speculation and debate concerning the chlamydial anomaly and are the strongest evidence to date that chlamydial species possess functional PG.