Chlamydiae are important pathogens and symbionts with unique cell biological 
features. They lack the cell-division protein FtsZ, and the existence of 
peptidoglycan (PG) in their cell wall has been highly controversial. FtsZ and PG 
together function in orchestrating cell division and maintaining cell shape in 
almost all other bacteria. Using electron cryotomography, mass spectrometry and 
fluorescent labelling dyes, here we show that some environmental chlamydiae have 
cell wall sacculi consisting of a novel PG type. Treatment with fosfomycin (a PG 
synthesis inhibitor) leads to lower infection rates and aberrant cell shapes, 
suggesting that PG synthesis is crucial for the chlamydial life cycle. Our 
findings demonstrate for the first time the presence of PG in a member of the 
Chlamydiae. They also present a unique example of a bacterium with a PG sacculus 
but without FtsZ, challenging the current hypothesis that it is the absence of a 
cell wall that renders FtsZ non-essential.