Electron micrographs of freeze-etched preparations of intact cells from (a)Geobacillus stearothermophilus PV72/p2 exhibiting oblique (p1) lattice symmetry, Bar, 50 nm, (b)Lysinibacillus sphaericus CCM 2177 showing a square (p4) lattice type, Bar, 150 nm, and (c)Thermoanaerobacter thermohydrosulfuricus L111-69 showing hexagonal (p6) lattice symmetry, Bar, 100 nm. Inserts: schematic drawings of the different S-layer lattice types. Depending on the lattice type, one morphological unit (shown in yellow) is composed of (a) one, (b) four, or (c) six identical subunits.