- Volume 20, Issue 4, 1970

Detailed knowledge of bacterial cell wall peptidoglycan structures has expanded rapidly in the past few years, and very definite patterns have emerged which can be attributed to common biosynthetic pathways, and, more speculatively, to a common structural function. The glycan is β - 1, 4 linked and is therefore a substituted form of chitin, probably retaining its linear conformation. The peptide may be more flexible, and varied in its cross-linking, but all contain a sequence derived from a probable common precursor, UDP- N- acetylmuramy 1-(A)- D - glu -(B)- D -ala- D - ala, when (A) and (B) are amino acids with the carboxy 1 and α-amino groups of a center with L - configuration in the main chain. The conformation of this sequence is discussed.

Cell wall preparations have been fractionated with hot formamide, lysozyme and lysozyme after pre-N- acetylation. Also trichloroacetic acid, cold or at 37°C, removes polysaccharides and teichoic acids. Dimethylhydrazine, or dilute alkali, also cause specific dissolution of some cell wall components. Isolation of purified specific polymers from the cell walls of bacteria grown in controlled conditions may provide valuable taxonomic information.

Review of the literature on the lipopolysaccharide of Enterobacteriaceae leads us to the following conclusions: (1) The structure of the peripheral portion, i. e. “O side chains,” varies extensively within each “genus.” (2) Although the structure of the central portion, i. e. “R core,” tends to be rather similar within each “genus,” there are cases of two Escherichia coli strains which synthesize the same O side chains and, at the same time, different R cores.

Cell walls of most Biotype 1 strains of V. fetus contained galactose and mannose; one type 1 strain had galactose and glucose. Cell walls of most Biotype 2 strains also had galactose and mannose; how-eger, some strains had galactose, glucose and mannose, some galactose alone and some galactose and rhamnose. Cell walls of most Biotype 3 strains had galactose and glucose; a few had galactose, glucose and mannose, or galactose alone. Whole cells of V. fetus contained small amounts of mesodiammopimelic acid (DAP), but meso-DAP could not be detected in purified cell walls.

Four groups of strains of Clostridia and anaerobic corynebacteria were examined by chemical and antigenic cell wall analysis. In each group it was possible to identify more than one pattern of cell wall sugar components, and these sugar patterns show a high degree of correlation with the subgroups revealed by cell wall agglutination tests. In the two groups tested, DNA/DNA homology tests showed that strains with the same cell wall sugar pattern had a high degree of homology (80-100%).

Deoxyribonucleic acid homology experiments among representatives of the clostridia and anaerobic corynebacteria generally correlate with the sugar composition and the isomeric form of diaminopimelic acid found in the cell walls and with the serological reactions. These correlations appear to be unique for a given group of bacteria and cannot be directly extended to others.

The distribution of diamino acids in cell walls of bacterial species bears some relation to taxonomy. The most widely distributed diamino acid is meso-diaminopimelic acid which is present in probably all Gram-negative species and in numerous other genera. L-lysine, also fairly common, is present in most Gram-positive cocci and in certain other species. Less frequent are DD or LL-diaminopimelic, β-OH - diaminopimelic, D or L ornithine, D or L diaminobutyric. The positions of these bifunctional amino acids in mucopep-tides (glycopeptides), the cross linked polymers of the walls, are described. Mucopeptides are divided into two types according to the site of termination of the cross-link from the D-alanine of an adjacent peptide chain. In type D, the site is the diamino acid which is located in the main peptide chain; in type G (less common) the site is the D-glutamic acid, and the diamino acid is in the cross link. Other differentiating features of types D and G include the optical configuration of the diamino acid, and the nature of the amino acid linking the peptide chain to the hexosamine backbone.

The information concerning the main components found in cell wall preparations and whole-cell hydrolysates of some 600 strains of aerobic actinomy-cetes is reviewed. The results show that whole-cell sugar patterns can usually be used to predict cell wall composition and that the combination of both criteria permit separation of aerobic actinomycetes into 10 taxonomically useful groups.

In consideration of the genera proposed for the family Actinomycetaceae, weighted considerations were given to the factors of morphology, carbon dioxide and oxygen utilization, anaerobic and aerobic fermentation balances, glucose metabolism, presence of catalase and haemoproteins, and cell wall composition. Primarily, on the basis of cell wall composition but strongly supported by metabolic and fermentation characteristics, it was concluded the genus Arachnia belongs in the family Propionibacteriaceae. Similarly, the genus Bacterionema is more suitable within the family Mycobacteriaceae or Corynebacteriaceae. The family Actinomycetaceae would retain Actinomyces israelii, A. bovis, A. naeslundii, A. odontolyticus, A. viscosus, and Rothia dentocariosa.

Structure and composition studies of cell walls of staphylococci and micrococci supports the classification of these organisms based on physiological and biochemical characters. Staphylococcus aureus and S. epidermidis are clearly separated as also are Micrococcus luteus and M. roseus.

A survey of the distribution of the various murein (peptidoglycan) types within the lactobacilli and related organisms is given. While all the species of some groups (thermobacteria, pediococci) contain only one type of murein, the species of other groups (beta-bacteria, bifidobacteria, leuconostoc) contain several types. The most common type, which occurs at least in a few species of most of the groups, is the Lys-Asp in which the crosslinkage of the peptide subunits is mediated by asparagine.

Specific antigens occur in many lactobacilli which group them in a similar way to their physiological and genetic characteristics. These group antigens may be located in the cell membrane or the cell wall, and may be teichoic acids or polysaccharides. Type antigens with a narrower specificity also occur and a cell membrane teichoic acid antigen common to all lactobacilli and to some other genera has been isolated.

General conventional phenotypic characteristics differentiating species and groups of Lactoba-cillus are reviewed. Newer approaches to taxonomic studies, such as cell wall structure, metabolic pathways of substrate utilization, enzyme activity and homology or heterology of enzyme structure, are discussed. Experiments and problems in lysing highly resistant cells to obtain DNA and RNA for nucleic acid homology studies are described.

Acid and aclohol products are extremely useful for identification of anaerobic bacteria. The types and relative amounts of products are similar from strain to strain (either fresh isolates or historic reference strains); reproducible from culture to culture within a strain; and easily determined by chromatography. Among the many different patterns of products, some, by definition, are shared by all species of the genus (e. g. Propionibacterium) and some are produced by only a single described species (e. g. Ramibacterium a alactolyticum).

In deciding on the importance of microbial characters much depends on the meaning attached to the word important, and this was discussed in relation to the subordination of characters, an old taxonomic principle in which different kinds of character were associated with different category levels.