The structure of the regular surface layer of Bacillus polymyxa has been examined to a resolution of 2.5–3.0 nm in electron micrographs of negatively stained preparations supplemented by optical-digital image enhancement. The layer is composed of morphological units, each consisting of four identical protein subunits, and has p4 symmetry with a = 10.0 nm. Within each unit cell are areas of high stain density of a limiting diameter of 2–3 nm, which are interpreted as holes penetrating the layer. A comparison is made with other tetragonal regular surface layers of spore-forming bacteria, B. sphaericus and Sporosarcina ureae, solved to 2.5-nm resolution. These layers are similar in the conformation of their protein units and in the distribution of the holes in the layer. A general scheme for the architecture of the tetragonal regular surface layers is derived.
Applications of Digital Image Enhancement Techniques for Improved Ultrasonic Imaging of Defects in Composite Materials
