FIGURE 1.

Bacterial glycans and architecture of the cell wall of different bacterial groups. Gram-negative bacteria (left part) contain a thin peptidoglycan layer, sandwiched between two cell membranes, and display LPSs (composed of lipid A, inner and outer core, and O-chain) anchored to the outer membrane. Gram-positive bacteria (middle part) contain a thick peptidoglycan layer, covering the cell membrane, and usually display teichoic acids anchored to the membrane (lipoteichoic acids) or bound to the peptidoglycan. Gram-negative and -positive bacteria may also present cell surface glycolipids, glycoproteins, and a polysaccharide capsule. Moreover, they may also secret different polysaccharides (known as exopolysaccharides) into the external environment. Representative exopolysaccharide structures of cepacian (produced by B. cepacia), alginate, and Psl (produced by P. aeruginosa) are shown in the inset. Mycobacteria (right part) contain a large cell wall complex formed by peptidoglycan, arabinogalactan, and mycolic acids of the so-called mycomembrane, and display other distinctive glycan structures, such as lipomannan, lipoarabinomannan, phosphatidyl-myo-inositol-mannosides, and trehalose mycolates. Sugar residues are depicted using the Symbol Nomenclature for Glycans (SNFG) (Varki et al., 2015; Neelamegham et al., 2019).