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

444 SCHLEIFER AND KANDLER
BACTERIOL. REV.
-G-M-G-
L-Ala
D-Gluu NH2
L-Orn - D-Ser. D- Asp 0a D- Ala
L- Ser- L-Ala- L-Thr-L-Ala - b
L-Ala - L-Ala- L- Ala C
D-Ala L- Orn
FIG. 22. Fragments of the primary structures of
ornithine-containing peptidoglycans of bifidobacteria
(A3f3 and A40). (a) L-Orn-D-Ser-D-Asp; (b)
L-Orn- L-Ser- L-Ala- L-Thr- L-Ala; (c) L-Orn- L-Ala3 .
L-Ser-L-Ala-L-Thr-L-Ala) is typical for the peptidoglycan
of B. longum (Fig. 22b, 200). It was
also detected in one strain of B. lactentis and
B. suis.
Strains of B. adolescentis contain either the
Lys-L-Ser-L-Ala2 type which is found in many
strains of Leuconostoc or the L-Orn-(L-Lys)-D-
Asp type which is typical for most of the lactobacilli.
The latter type, however, differs from
that of lactobacilli, since L-Orn and L-Lys are
both present in varying amounts in the same
peptidoglycan. The ratio of Orn/Lys varies
with different strains of B. adolescentis, but is
not influenced by exogenous addition of Lys or
Orn.
A similarly varying ratio of Lys and Orn was
found in strains isolated from the rumen of the
sheep (145). These strains were recently described
as a new species B. globosum (330). The
interpeptide bridge here consists of a tri-L-alanine
peptide (Fig. 22c).
B. indicum and B. coryneforme contain the
L-Lys-D-Asp type as do many strains of lactobacilli
and some streptococci. The peptide
subunits of the peptidoglycans of B. ruminale
and B. thermophilum are also cross-linked by a
D-dicarboxylic amino acid, namely D-Glu as in
the genus Planococcus (340, Fig. 18a). These
two species are most likely identical.
Family Bacillaceae. This group of sporeforming,
gram-positive rods is subdivided into
two genera: the aerobic or microaerophilic
strains are included in the genus Bacillus, the
anaerobic organisms in the genus Clostridium.
Genus Bacillus. The vast majority of the
strains of the genus Bacillus belong to the same
peptidoglycan type, namely the directly crosslinked
m-Dpm type (Aly, Fig. 6). The species
showing this type are listed in Table 29. The
peptidoglycan of a few of these species have
been studied in greater detail (Fig. 23). The
exact structure of B. megaterium KM was
established by Bricas et al. (50), that of B.
licheniformis by Hughes (146, 147), and that of
B. subtilis by Warth and Strominger (402). H.
Ranftl in our laboratory (H. Ranftl, Ph.D.
thesis, Technical University, Munich, 1972)
has also studied in detail a large number of cell
walls ot' various bacilli. Despite the similarity in
the primary structure of their peptidoglycan,
there are differences in the amidation of carboxyl
groups, the degree of cross-linkage, the
chain length of peptide subunits, and the occurrence
of D, i)-Dpm besides m-Dpm. Most of
the bacilli contain only one amide group in the
peptidoglycan; either the a-carboxyl group of'
D-Glu can be amidated as in the case of' B.
licheniformis (254) or the carboxyl group of
m-Dpm which is not involved in a peptide bond
is amidated as in the case of B. subtilis (402).
Some bacilli have no amide group at all, e.g., B.
megaterium (50), B. lentus, and B. firmus (H.
Ranftl, Ph.D. thesis, Technical University, Munich,
1972). In the peptidoglycan of B. megaterium,
besides m-Dpm residues, D,D-Dpm residues
were also found (50). The D, D-Dpm
residues seemed to be involved in another mode
of crdss-linkage (370). The D, D-Dpm residues
may replace a D-Ala residue by a transpeptidation
reaction at the C terminus of a peptide
subunit and can connect with an adjacent
peptide subunit so that a cross-linkage is
f'ormed between an amino group of D,D-Dpm
and a carboxyl group of a D-Ala residue.
The peptide subunits usually consist of tetraor
tripeptides and, sometimes pentapeptides
can also occur. The ratio of tetra- to tripeptides
can vary from strain to strain. A high content of
tripeptides is paralleled by a low degree of
cross-linkage. These different variations of the
directly cross-linked, m-Dpm-containing peptidoglycan
may be characteristic for the various
species, but it is still too early for a taxonomic
evaluation. Another helpful feature for the
grouping of bacilli may be the composition of
the polysaccharide and teichoic acid polymers
of the cell walls. Very often glycerol-containing
teichoic acids are found in cell walls of bacilli
(H. Ranftl, Ph.D. thesis, Technical University,
Munich, 1972), whereas ribitol teichoic acids
are rather uncommon and have been detected
as yet only in B. subtilis (20, 21). Teichuronic
acid was found in B. licheniformis (148). Besides
these anionic polymers, neutral polysaccharides
also occur which can be composed of
amino sugars such as glucosamine, galactosamine,
or mannosamine, or all three, and other
sugars such as glucose, galactose, or mannose,
or all three.
A few unique bacilli characterized by the
production of spherical endospores have a different
type of peptidoglycan. B. sphaericus
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