Peptidoglycan .Types of Bacterial Cell Walls and their Taxonomic ...

408 SCHLEIFER AND KANDLER
BACTERIOL. REV.
One of the basic markers for the differentiation
of bacteria is the so-called Gram reaction.
The gram-positive bacteria are distinguished by
their ability to hold back the dye-iodine complex,
whereas the gram-negative organisms are
decolorized after treatment with alcohol. The
mechanism of the Gram reaction has not yet
been unraveled, but Salton (326) favors an
involvement of the cell wall and has suggested a
permeability difference between the cell walls
of gram-positive and gram-negative bacteria as
the basis for the Gram reaction. This is in
agreement with the findings that the positive or
negative response to this reaction is reflected in
the different ultrastructure of the cell wall. The
cell wall of a gram-positive bacterium shows in
profile one thick and more or less homogenous
layer, whereas the profile of the cell wall of a
gram-negative bacterium is remarkably complex
and consists of several layers. A number of
excellent monographs and reviews have recently
appeared (see references 57, 89, 118, and
269 for more detailed information).
The polymers making up the cell walls are
chemically quite different in these two groups
of bacteria. The gram negatives contain as
major components lipopolysaccharide, lipoprotein,
and relatively little peptidoglycan (less
than 10% of the total cell wall) in their cell
walls, whereas the walls of gram positives are
mainly composed of peptidoglycan (usually
30-70% of the total cell wall), polysaccharides
or teichoic acid (or both), or teichuronic acid.
The peptidoglycan is the only cell wall polymer
common to both gram-negative and
gram-positive bacteria. It has also been found
among blue-green algae (96, 102, 142). Thus
peptidoglycan is a cell wall component of all
procaryotic organisms. There are only a few
halophilic bacteria, such as Halobacterium halobium
(326, 363) and Micrococcus morrhuae
(177), which lack peptidoglycan. The composition
and structure of the peptidoglycan seem to
be rather constant among gram negatives, but
there is great variation among gram positives.
Numerous reviews have recently appeared on
the structure and biosynthesis of the peptidoglycan
(109, 117, 237, 279, 284, 333, 354, 381,
386, 403, 426). Since that time our knowledge
about the diversity of the chemical structure
of the peptidoglycan has increased. Moreover,
a high percentage of all known genera
and of many different species of bacteria has
been examined, and it now seems worthwhile
to focus on the correlation of peptidoglycan
structure and taxonomy. Therefore, in the
first part of this review a classification of the
known peptidoglycan types based on their
mode of cross-linkage will be suggested. In the
second part, the distribution of the various
peptidoglycan types within the bacterial kingdom
will be shown and their taxonomic significance
will be evaluated.
The following are abbreviations and uncommon
amino acids and amino sugars used
throughout the paper. Abbreviations: ATCC,
American Type Culture Collection, Rockville,
Md., U.S.A.; CCM, Czechoslovak Collection of
Microorganisms, J. E. Purkyne University,
Brno, Czechoslovakia; Kiel, Streptokokkenzentrale
im Institut fur Milchhygiene der Bundesanstalt
fur Milchwirtschaft, Kiel, BRD;
NCDO, National Collection of Dairy Organisms,
Reading, England; NCIB, National Collection
of Industrial Bacteria, Aberdeen, Scotland;
NCPP, National Collection of Plant Pathogenic
Bacteria, Harpenden, England;
NCTC, National Collection of Type Cultures,
London, England. Amino acids and amino
sugars: GlcNH2 or G, glucosamine; Dab, diaminobutyric
acid; m-Dpm, meso-diaminopimelic
acid; Hsr, homoserine; HyDpm, hydroxydiaminopimelic
acid; Hyg, threo-3-hydroxyglutamic
acid; HyLys, hydroxylysine; Mur or
M, muramic acid; Orn, ornithine.
DIFFERENT PRIMARY
STRUCTURES OF THE
PEPTIDOGLYCAN
General Structures
The rigidity of the bacterial cell wall is due to
a huge macromolecule (403) containing acylated
amino sugars and three to six different
amino acids. This polymer has been called by a
variety of names: "basal structure" (425), "mucopeptide"
(232), "glycopeptide" (365), "glycosaminopeptide"
(326), "murein" (403), and
"peptidoglycan" (369). We have usually prefered
to use the name "murein," which was
introduced by Weidel and Pelzer (403) in analogy
to "protein." But there is now a general
agreement that "peptidoglycan" is the better
term, since it describes the chemical nature of
this polymer most exactly. Peptidoglycan is a
heteropolymer built out of glycan strands crosslinked
through short peptides. The general
features of the two peptidoglycan constituents,
the glycan and the peptide moiety, will be
separately discussed first.
Glycan strands. The glycan moiety of the
peptidoglycan is remarkably uniform. It is
usually made up of alternating f,-1,4-linked
N-acetylglucosamine and N-acetyl muramic
acid residues (109, 111). The latter amino sugar,
found only in bacteria and blue-green algae, was
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