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

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VoL- 36, 1972 PEPTIDOGLYCAN TYPES OF BACTERIAL CELL WALLS 417 cross-linkage." For many years it was only known to occur in the very widespread m- Dpm containing peptidoglycans. Recent investigations on the peptidoglycan structure of aerococci, several streptococci, and of Spirochaeta have shown that direct cross-linkage can also occur in bacteria containing L-Lys or L-Orn instead of m-Dpm. Thus, we can distinguish three variations within subgroup Al: variation Ala with L-Lys; variation Al , with L-Orn; variation Al y with m-Dpm in position 3 of the peptide subunit (Table 5). The m-Dpmcontaining variation may be subdivided in types TABLE 5. Variations and types of subgroup Al depending on the amidation of the free carboxyl groups of the peptide subunits (Table 5). In E. coli and Bacillus megaterium, none of the carboxyl groups are amidated. In B. licheniformis ATCC 9945 the a-carboxyl group of D-Glu is substituted, whereas in B. licheniformis NCTC 6346 and in B. subtilis most of the peptide subunits have an amide substituent on the carboxyl group of the D-asymmetric carbon of m-Dpm. Cell walls of Lactobacillus plantarum and Corynebacterium diphtheriae have both carboxyl groups amidated. It should, however, be mentioned that the extent of amidation Varia- Diamino Amidation of peptide subunit Species Fig. Reference tion acid Ala L-Lys Partly amidated Aerococcus viridans, Gaffkya 18 268 homari ATCC 10400 All L-Om Not amidated Spirochaeta stenostrepta 28 Schleifer and Joseph, manuscript in preparation A1y m-Dpm Not amidated Escherichia coli, Bacillus 6 394 megaterium One carboxyl group amidated (a) a-Carboxyl group of D-Glu Bacillus licheniformis ATCC 6 254 9945 (b) Carboxyl group of m-Dpm B. subtilis, B. licheniformis 6 148, 402 NCTC 6346 |Hothcarboxyl groupsamidated |Lactobacillus plantarum, Co- 6 242,406,188 B rynebacterium diphtheriae 1 TABLE 6. Peptidoglycan types of variation A3aa Position 4 Interpeptide bridge Position 3 Species Fig. Reference -Gly - Bifidobacterium 23 176 Gly6-- Staphylococcus aureus Copenhagen 8 113 Gly(L-Ser) _ Micrococcus mucilaginosus 16 Schleifer et al., manuscript in preparation L-Ala(L-Ser) t M. mucilaginosus 16 Schleifer et al., manuscript in preparation D-Ala L-Ala a - L-Lys Arthrobacter crystallopoietes 21c 210, 211 i L-Ala2 - L. coprophilus 21c 144 L-Ala,3 M. roseus 13 293 Streptococcus thermophilus a 336 -L-Ala4- A. ramosus 13a 101 L-Ala, - Micrococcus sp. 7425 Schleifer, unpublished data a Interpeptide bridges consist of single amino acids or homo-oligopeptides. Downloaded from http://mmbr.asm.org/ on December 3, 2012 by guest
418 SCHLEIFER AN4D KANDLER BACTERIOL. REV. can be decreased by enzymic reactions (148a, 188). Besides this variation in the amidation, there is also a variation in the length of the peptide subunit due to the variable occurrence of D-Ala carboxypeptidases. If these enzymes are present, peptide subunits consisting of tripeptides (lacking D-Ala) are found besides tetrapeptides (206, 242, 386, 402). In case of L. plantarum both carboxyl groups of m-Dpm in the tripeptides are amidated. A fragment of the primary structure of subgroup A2 (cross-linkage by polymerized peptide subunits) is depicted in Fig. 7. This subgroup shows several peculiarities. (i) At least 50% of the N-acetylmuramic residues are not substituted by a peptide subunit (220, 265). (ii) All of the glycine residues in the native cell walls are C-terminal (388, 389). Therefore, Gly is not involved in the cross-linking of the peptide subunits but is bound to the a-carboxyl group of D-Glu (189, 253). (iii) Eighty percent of the E-amino groups of L-Lys are unsubstituted. The primary structure of the peptidoglycan was first established by studies in our own laboratory (338) and later confirmed and refined by the work of Ghuysen's group (116). According to these findings, the peptide subunits are connected through bridges which are formed by a "head-to-tail" linkage of several peptide subunits. Thus, the peptide subunits are linked together through polymerized peptide subunits. Up to four peptide subunits can form the connecting bridge. Subgroup A2 may be understood as a further development of the directly cross-linked variation of Ala. Besides the substitution of the a-carboxyl group of D-Glu by Gly, the only difference from the directly cross-linked variation is an additional biosynthetic step as proposed by Schleifer and Kandler (338): that is an amidase reaction in which the amide linkage between N-acetylmuramic acid and L-Ala is -G-M-G- L- Ala D-Glu -Gly p L- Lys*e Gly D-Ala-L-Lys*-
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