THE GEOMETRY AND OSMOTIC RELATIONS OF PLASMOLYSIS SPACES IN BACTERIA AND THE ROLE OF ENDOCYTOSIS, TUBULAR STRUCTURES AND SCHEIE STRUCTURES IN THEIR FORMATION

When bacterial cells are subject to an osmotic ''up-shock'', water flows out from the cell through the cytoplasmic membrane (CM), murein (M), and outer membrane (OM). Lipid bilayers can shrink very little in area and therefore must wrinkle to accommodate the smaller volume of cytoplasm. Plasmolysis spaces an formed if the CM separates from the M and OM. However, because the CM bilayer is essentially an incompressible two-dimensional liquid, this geometric constraint restricts the location and shape of plasmolysis spaces. Without change in bilayer surface area, they can form only at the pole and around constricting regions in the cell. Elsewhere creation of plasmolysis spaces requires the formation of endocytotic or exocytotic vesicles, tubular structures, or other special geometric shapes to remove bilayer area from the CM surrounding the cytoplasm. Vesicles, tubular structures (Bayer adhesion sites), and Scheie structures (of cytoplasm of non circular cross-section) are observed in the electron microscope. These may have smooth surfaces, but after severe osmotic up-shocks, rough surfaces of the CM persist. This paper reviews the generality of endocytotic vesicle formation in animal, plant and bacterial cells and the mechanical properties of lipid bilayers. It then discusses the role of the vesicles and of tubular structures in plasmolysis space formation, and analyzes the geometric problem of the formation of plasmolysis spaces when the area of the CM is invariant. The distribution of initial sites of plasmolysis, the periseptal annulus model, the leading edge model, the volume of the normal periplasmic space, and osmotic pressure of the periplasmic space are also considered. (C) 1995 Academic Press Limited