The biosynthesis and functionality of the cell-wall of lactic acid bacteria

The cell wall of lactic acid bacteria has the typical Gram-positive structu re made of a thick, multilayered peptidoglycan sacculus decorated with prot eins, teichoic acids and polysaccharides, and surrounded in some species by an outer shell of proteins packed in a paracrystalline layer (S-layer). Sp ecific biochemical or genetic data on the biosynthesis pathways of the cell wall constituents are scarce in lactic acid bacteria, but together with ge nomics information they indicate close similarities with those described in Escherichia coli and Bacillus subtilis, with one notable exception regardi ng the peptidoglycan precursor. In several species or strains of enterococc i and lactobacilli, the terminal D-alanine residue of the muramyl pentapept ide is replaced by D-lactate or D-serine, which entails resistance to the g lycopeptide antibiotic vancomycin. Diverse physiological functions may be a ssigned to the cell wall, which contribute to the technological and health- related attributes of lactic acid bacteria. For instance, phage receptor ac tivity relates to the presence of specific substituents on teichoic acids a nd polysaccharides; resistance to stress (UV radiation, acidic pH) depends on genes involved in peptidoglycan and teichoic acid biosynthesis; autolysi s is controlled by the degree of esterification of teichoic acids with D-al anine; mucosal immunostimulation may result from interactions between epith elial cells and peptidoglycan or teichoic acids.