Structures of exopolysaccharides and capsular polysaccharides (CPSs and EPSs). Like O-antigenic polysaccharides, the structures of CPS and EPS are highly diverse, and the main structural features are covered by the examples shown. The structures are divided according to the three main assembly mechanisms. One group of CPSs is formed by a pathway involving an ATP-binding cassette (ABC) transporter and is (so far) confined to Gram-negative bacteria. The hallmark of this system is the presence of a conserved glycolipid anchor containing an oligosaccharide of β-linked Kdo. Most CPSs with complex branched structures in Gram-negative and Gram-positive bacteria use a conserved mechanism that requires a characteristic polymerase protein, designated Wzy. Relatively simple structures involved in biofilm formation (e.g., cellulose and poly-N-acetylglucosamine or PNAG) and some glycosaminoglycans use a pathway involving a dual polymerase-exporter protein referred to as a synthase. D-AAT, 2-acetamido-4-amino-2,4,6-trideoxygalactose.