State of the rigid-layer in cell walls of some gram-negative bacteria

Summary Rigid-layers in cell walls of Enterobacteriaceae and Pseudomonadales contain murein sacculi of identical chemotype. However, lipoprotein in covalent linkage to the murein participates to a different extent in rigid layer construction in the two taxonomic groups. In Proteus mirabilis and Escherichia coli lipoprotein particles of similar size and spatial arrangement are visible in the electron microscope as major rigid layer components. In the cell walls of Pseudomonadales covalent (lipo-)protein plays a far less prominent role. It is present as a minor constituent in rigid layers of Pseudomonas aeruginosa. Rigid layers of Spirillum serpens are naked murein sacculi devoid of any covalently attached protein.