Homopolysaccharides from lactic acid bacteria

In addition to heteropolysaccharides of complex structure, lactic bacteria produce a variety of homopolysaccharides containing only either D-fructose or D-glucose. These fructans and glucans have a common feature in being synthesized by extracellular transglycosylases (glycansucrases) using sucrose as glycosyl donor. The energy of the osidic bond of sucrose enables the efficient transfer of a D-fructosyl Or D-glucosyl residue via the formation of a covalent glycosyl-enzyme intermediate. In addition to the synthesis of high molecular weight homopolysaccharides, glycansucrases generally catalyse the synthesis of low molecular weight oligosaccharides or glycoconjugates when efficient acceptors, like maltose, are added to the reaction medium. While the enzymatic synthesis of fructans (levan and inulin) is poorly documented at the molecular level, the field of Streptococcus and Leuconostoc glucansucrases (glucosyltransferases and dextransucrases) has been well studied, both at the mechanistic and gene structure levels. The nutritional applications of the corresponding polysaccharides and oligosaccharides account for this increasing interest. (C) 2001 Elsevier Science Ltd. All rights reserved.