Ultrastructural properties of the extra membranes of Escherichia coli O111a as revealed by freeze-fracturing and negative-staining techniques.

Escherichia coli O111a is a thermosensitive strain which, when grown at 40 C, accumulates large quantities of intracellular membranes. The ultrastructure of these membranes in cells which have been chemically fixed, embedded, and examined as thin sections has been compared with that of membranes in cells negatively stained or freeze-fractured. Results indicate that the extra membranes are present in the three types of preparations examined and, therefore, clearly are not artifacts of chemical fixation. Negative staining has proved also to be a valuable tool as a rapid means of monitoring cells for the accumulation of large amounts of extra membranes. Also, examination of thin sections has shown that distinct continuities between the plasma membrane and the extra membranes exist. In general, membrane surfaces in freeze-fractured cells containing extra membranes appear smooth and lack the particles associated with the plasma membranes of many cells.