The partial chemical degradation of the cell walls of Lactobacillus plantarum, Streptococcus faecalis, and Lactobacillus casei.

The cell wall of a bacterium is generally understood, at the cytological level, to be a rigid outer layer which gives the organism its characteristic size and shape and does not include the extracellular slime or capsule so often encountered among bacterial species. The “microcapsule,” a term of convenience for immunologically but not morphologically demonstrable properties of the bacterial surface, also is not considered part of the cell wall proper (2). The chemical composition of wall preparations may depend in part upon the operations and conditions used in their isolation. In our previous study (3) we have included the ribonuclease, trypsin, and pepsin digestion steps of Cummins and Harris (4) as part of our cell wall isolation procedure. Although this enzymatic digestion would solubilize any nonrelated protein contaminants, the possibility of partial degradation of integral cell wall components is not excluded. The removal of “microcapsular” components from cell wall preparations of type 14, group A hemolytic streptococcus by tryptic digestion, or even simple extraction with water, has been clearly demonstrated by Barkulis and Jones (5). Furthermore, Brown (6) has shown that treatment as mild as lyophilization is sufficiently drastic to render part of the cell wall of Streptococcus faecalis and of a Pseudomonas species subsequently soluble in water, presumably through disturbing its hydrogen bond structure. In spite of the difficulty of determining when, and to what extent, degradation of the native cell wall may have taken place, it is clear from a number of studies that bacterial cell walls are heteropolymeric in nature (2). We are concerned at the present with the gram-positive organisms. A type of polymer occurring in a number of bacterial cell walls is the unusual trichloroacetic acid-soluble teichoic acid described by Armstrong et al. (7) that contains either a ribitol phosphate or glycerol phosphate backbone and has reducing sugars or amino sugars and alkali-labile n-alanine as substituents. Recently, Janczura et al. (8) have described a different type of polymer from Bacillus subtilis cell wall, a wall which also contains a teichoic acid moiety (9). This substance contains equimolar amounts of glucuronic acid and N-acetylgalactosamine and the name teichuronic acid has been suggested for it. A structure which seems to be a common, if not universal, feature in walls of gram-positive organisms is an insoluble pep-