THE FRACTURE-FLIP TECHNIQUE REVEALS NEW STRUCTURAL FEATURES OF THE ESCHERICHIA-COLI CELL-WALL

With few exceptions, all bacteria possess a wall which protects them a nd controls their communication with the environment. In Gram-negative bacteria the cell wall exhibits a complex and unique multilayered org anization. We hare applied a modification of the freeze-fracture techn ique known as 'fracture-flip' to visualize the real surfaces of the di fferent wall layers in a Gram-negative bacterium, Escherichia coli, In combination with treatments to weaken the interlayer connections. thi s technique has provided new insights into the structure of the bacter ial wall. Large areas of an intermediate layer (most probably the pept idoglycan-containing matrix) have been visualized for the first time b etween the plasma membrane and the outer membrane of the wall, Extensi ve regions corresponding to the cytoplasmic face of the plasma membran e have also been obtained. These images provide new three-dimensional views of the bacterial cell wall and provide the structural framework for the analysis of the molecular relationships between the different cell wall components.