4-3. Cell wall structure of E. coli and B. subtilis

The structure of peptidoglycans of Escherichia coli and Bacillus subtilis is similar except for a few minor modifications, but murein (cell wall) structures are extremely different because the major cell wall constituents, anionic polymers, are not attached to peptidoglycans of E. coli but are attached to those of B. subtilis. Thickness of the cell walls in B. subtilis and the presence of an outer membrane in E. coli are other important differences in the cell wall. In E. coli, murein hydrolases have several functions such as being associated with peptidoglycan biosynthesis, cell separation, modification and recycling/turnover of the cell wall components. In B. subtilis, further various functions include association with cell lysis, cell motility, prophage-induced autolysis, competence, conjugation, lateral peptidoglycan expansion/modification, and sporulation and germination. Enzymatic properties and functions of peptidoglycan hydrolases and cell wall recycling enzymes are reviewed. Moreover, functions and biosynthesis of anionic polymers (teichoic acid, teichuronic acid, and lipoteichoic acid) are fully described.