Bifdobacterial exopolysaccharides: a brief review

Abstract

Exopolysaccharide (EPS) production is a widespread phenotypic trait in many commensal and pathogenic microorganisms. In bifidobacteria, the discovery of the eps gene cluster propelled the multiple studies of their EPS, which represent heteropolysaccharides and generally consist of three monosaccharides: D-glucose, D-galactose, and L-rhamnose. EPS of B. animalis subsp. lactis additionally contains mannose while EPS of B. adolescentis and B. longum subsp. longum contains 6-deoxytealose. The number of repeat units in bifidobacterial EPS is a straincharacteristic feature. Precursors of the indicated EPS monomers are glucose-1-phosphate and fructose-6-phosphate, and the synthesis involves nucleotide sugar intermediates. Two molecular systems are implica in polymerisation and polymer secretion in bifidobacteria: ABC transporters and fippase polymerase complex (Wzx/Wzydependent pathway). EPS perform numerous functions. They protect bifidobacteria from aggressive gastrointestinal milieu and reactive oxygen species, provide a scaffold for the bacterial-bacterial interactions, and act as the receptors for phage adsorption. Further, EPS are used by the other members of the gut microbiota as substrates for nutrition, i.e. bifidobacteria regulate the composition and metabolic activity of intestinal microorganisms. Therefore, EPS-producing strains exhibit pronounced antibacterial effects due to the binding of opportunistic and pathogenic microbes. Finally, EPS can act as pathogen-associated molecular patterns. Beneficial effects of bifidobacterial EPS determined the possibility of their use as prebiotics or as a part of symbiotics. The main limitation in this regard is the low yield of the target product when culturing EPS-producing strains. Therefore, current research is aimed at finding novel EPSproducing strains among the bifidobacteria and creating favorable technological conditions that promote EPS production.