Characterization of Bacterial Exopolysaccharides

The present study investigated the structural characterization of exopolysaccharides (EPS) produced by Campylobacter jejuni, Bifidobacterium animalis subsp. lactis and a number of Bifidobacterium breve strains. Nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography coupled with multiangle laser light scattering (SEC-MALLS), anion exchange chromatography, HPAEC-PAD analysis, monomer and linkage analysis employing GC-MS have been used to characterise the EPS structures.

Monomer analysis of the EPS produced by Campylobacter jejuni showed the presence of glucose, linkage analysis showed the presence of an �-(1�6) glycosidic linked repeating monomer unit and NMR (1D- and 2D- experiments) showed that the EPS is an �-dextran.

NMR and size exclusion chromatography analysis for B. animalis subsp. lactis shows the presence of a complex mixture of EPS. Monomer analysis for different batches suggests that each contains variable amounts of rhamnose, glucose and galactose along with trace levels of mannose. The results of the linkage analysis indicate that a complex mixture of differently linked sugars is present including : terminal rhamnose, 1,2-linked rhamnose, 1,3-linked rhamnose, terminal hexoses, 1,2,3-linked rhamnose, 1,4-linked hexose, 1,3-linked hexose, 1,6-linked hexose, Nacetyl sugars and 1,3,4-linked hexoses. SEC-MALLS showed the presence of different molecular weight EPSs. Uronic acid analysis showed that in 5.0 mg of EPS sample, only 0.28 mg of uronic acid is present.

1D- and 2D-NMR experiments were performed on the EPS samples produced by B. breve strains including UCC2003, JCM7017, JCM7019 and NCFB2258. Analysis of EPS extracted from cells using sodium hydroxide (NaOH) showed that complex mixtures of polysaccharides were being recovered. However, a common set of NMR signals was present in all the EPS samples from B. breve. Analysis of this set of signals suggests that, on treatment of cells with NaOH, a �-(1�6)-linked glucan is released from a variety of bifidobacterial strains.