Topological features of membranes from Staphylococcus aureus and Acholeplasma laidlawii

Topological and ultrastructural features of membranes from walled and wall-less bacterial cells were compared by examining membranes from Staphylococcus aureus and Acholeplasma laidlawii. Osmotic lysis of protoplasts of S. aureus or cells of A. laidlawii produced membrane vesicles or large membrane fragments, but alumina grinding or sonication of these protoplasts or cells produced much smaller particles whose morphologic origin was difficult to determine. Disrupted membranes from either organism were covered with ribosomes from 15 to 30 nm diameter adhering almost exclusively to the inside of the vesicles or fragments. Membranes were similar in thickness and possessed 5--6 nm globular knobs which were not on stalks, not highly ordered, and easily differentiated from the negative-stained background. Although the globular knobs were regularly visible on membrane sheets from S. aureus, they were seen on A. laidlawii membrane vesicles only rarely unless the membrane vesicles were treated with 0.01% saponin or 90% (v/v) cold acetone, which extracted lipids and glycolipids from the membrane vesicles. Membrane vesicles from lysed cells of A. laidlawii showed a widespread distribution of circular pits about 10 nm deep and at least 20-30 nm across, not seen in lysed protoplast membranes of S. aureus.