Formation of flat lamellar intramembrane lipid structures in microorganisms

Analysis of freeze-fracture replicas and thin sections of cells of the bact eria Sulfobacillus thermosulfidooxidans and Anaerobacter polyendosporus sho wed that their cytoplasmic membranes contain some regions in the form of fl at lamellar inverted lipid membranes a few tenths of nanometers to a few mi crons in size. The specific features of these membrane structures are as fo llows: (i) they contain no familiar intramembrane particles commonly presen t on freeze-fracture replicas; (ii) in cross thin sections, intramembrane s tructures are bifurcate 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 cultivat ed under normal growth conditions. The data obtained suggest the occurrence of a complex type of compartmentalization in biological membranes.