(a) Synechococcus (strain WH8113). Membrane fracture uncovering the inner cell membrane (CMi) showing a dense distribution of intramembrane particles. Fracture plane then crosses the surface layer (S) into the surrounding medium showing spicules (arrowhead) that extend from the cell surface. Arrow shows fiber extending from outer membrane to cell membrane. Scale bar, 100 nm. (b) Synechococcus (strain WH8113) Complementary fracture plane showing the outer leaflet of the cell membrane (CMo) which has fewer intramembrane particles than the inner leaflet. The fracture then crosses to the outer leaflet of the outer membrane (OMo), and then turns to fracture across the surface layer (S). Scale bar, 100 nm.