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 flo ws out from the cell through the cytoplasmic membrane (CM), murein (M) , and outer membrane (OM). Lipid bilayers can shrink very little in ar ea and therefore must wrinkle to accommodate the smaller volume of cyt oplasm. Plasmolysis spaces an formed if the CM separates from the M an d OM. However, because the CM bilayer is essentially an incompressible two-dimensional liquid, this geometric constraint restricts the locat ion 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 for mation of endocytotic or exocytotic vesicles, tubular structures, or o ther special geometric shapes to remove bilayer area from the CM surro unding the cytoplasm. Vesicles, tubular structures (Bayer adhesion sit es), and Scheie structures (of cytoplasm of non circular cross-section ) are observed in the electron microscope. These may have smooth surfa ces, but after severe osmotic up-shocks, rough surfaces of the CM pers ist. This paper reviews the generality of endocytotic vesicle formatio n in animal, plant and bacterial cells and the mechanical properties o f lipid bilayers. It then discusses the role of the vesicles and of tu bular structures in plasmolysis space formation, and analyzes the geom etric 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 t he normal periplasmic space, and osmotic pressure of the periplasmic s pace are also considered. (C) 1995 Academic Press Limited