Architecture of peptidoglycan: more data and more models.

Peptidoglycan forms a net-like sacculus made of glycan strands crosslinked by peptides. The length of the glycan strands and the degree of crosslinkage vary with bacterial species, strains and growth conditions. Several models for the three-dimensional architecture of peptidoglycan have been proposed, some of which have been tested experimentally. The new data support a layered model in Gram-negative bacteria, and a more elaborate peptidoglycan architecture, with bands made of coiled bundles of glycan strands, in the rod-shaped Bacillus subtilis. However, many questions remain unanswered and, therefore, more data and more models are required to decipher the complex cell wall architecture in bacteria.