An Electron Diffraction Study of the Structure and Orientation of the Lipids in Yeast and Bacterial Cell Walls

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Abstract
The structure and orientation of the lipids in the cell walls of yeast, Staphylococcus aureus and Escherichia coli, has been studied by light microscopy, electron microscopy and electron diffraction methods. When fat solvents are applied to the hydrated cells in aqueous suspension, the cell walls are weakened owing to the displacement of fat-soluble lipids. If yeast cells are allowed to dry on a glass surface, the degree of cell flattening is proportional to the degree of lipid displacement. The dried fat-soluble and bound lipids of the cells both show the hexagonal crystalline structure, but a proportion of the bound lipids shows the more condensed orthorhombic structure. The correlation between the degree of cell flattening and of diffraction pattern intensification shows that there is a preferred orientation of lipid crystals in the superficial layers of the dried cells. The hydrocarbon chains of the lipids are normal to the cell surface, so that a higher proportion of chains is parallel to the electron beam in extracted cells (the cells are flattened in a plane at right angles to the beam), although the total quantity of lipid present has been reduced by treatment with fat solvent. If flattening did not occur, there should be a weakening of the diffraction pattern, owing to a decrease in the amount of lipid present. The analogy between the structure of the lipids in the cell wall and in the Calliphora pupal skin is discussed.