Formation of flat lamellar intramembrane lipid structures in microorganisms

Analysis of freeze-fracture replicas and thin sections of cells of the bacteria Sulfobacillus thermosulfidooxidans and Anaerobacter polyendosporus showed that their cytoplasmic membranes contain some regions in the form of flat lamellar inverted lipid membranes a few tenths of nanometers to a few microns in size. The specific features of these membrane structures are as follows: (i) they contain no familiar intramembrane particles commonly present on freeze-fracture replicas; (ii) in cross thin sections, intramembrane structures are bi-furcate on the periphery and look like thylakoids; and (iii) the leaflets of intramembrane structures in S. thermosulfidooxidans cells are corrugated. These structures were revealed in bacterial cells cultivated under normal growth conditions. The data obtained suggest the occurrence of a complex type of compartmentalization in biological membranes.