Morphology and Chemistry of Cell Walls ofMicrococcus radiodurans

Abstract

Walls of the pigmented strain of M. radiodurans showed several layers in the electron microscope. These layers include an outermost network structure removed by trypsin, a fragile soft layer containing hexagonally packed subunits, and a rigid layer penetrated by numerous holes. The 2 inner layers were separated by a process of autolysis, trypsin treatment, and gradient centrifugation. The hexagonally packed layer was less dense, pink in color, and it contained carotenoids, lipid, protein, and polysaccharide. The lipid consisted of odd-numbered as well as even-numbered fatty-acids, and the polysaccharide contained rhamnose and mannose, but it did not contain heptose. The "holey" layer was white and was composed of a mucopeptide containing glucosamine and muramic acid. The main amino-acids in the "holey" layer were glutamic acid, alanine, glycine, and L-ornithine, in the ratios of 1:1.7:1.8:1.2, respectively. This layer also contained phosphorus, glucose, and a trace of meso- and LL-diaminopimelic acid. A white mutant, W1, of M. radiodurans had no pigment or lipid in its walls, but it contained small amounts of the "hexagonal" layer. The holey layer, constituting the bulk of the wall, was similar in morphology and composition to that layer in the pigmented strain. Lysozyme did not remove the lipoprotein-poly-saccharide component from the walls of the pigmented strains, and the hexagonally packed structure was not visibly affected, except for change in a minor structure. Most of the mucopeptide layer was solubilized by lysozyme, but a structureless bag-shaped residue was left. This residue contained phosphorus, carbohydrate, and limited amino-acids, but it did not contain muramic acid, glucosamine, or ornithine. Aqueous phenol removed a lipoprotein component from strain R1, which contained limited fatty-acids. It also removed meso-and LL-diaminopimelic acid.