Structure of the high molecular weight exopolysaccharide produced by Bifidobacterium animalis subsp. lactis IPLA-R1 and sequence analysis of its putative eps cluster.

The bile adapted strain Bifidobacterium animalis subsp. lactis IPLA-R1 secretes a high molecular weight exopolysaccharide (HMW-EPS) when grown on the surface of agar-MRSC. This EPS is composed of L-rhamnopyranosyl, D-glucopyranosyl, D-galactopyranosyl and D-galactofuranosyl residues in the ratio of 3:1:1:1. Linkage analysis and 1D and 2D NMR spectroscopy were used to show that the EPS has a hexasaccharide repeating unit with the following structure: [See formula in text]. Treatment of the EPS with mild acid cleanly removed the terminal d-galactofuranosyl residue. The eps cluster sequenced for strain IPLA-R1 showed high genetic homology with putative eps clusters annotated in the genomes of strains from the same species. It is of note that several genes coding for rhamnose-precursors are present in the eps cluster, which could be correlated with the high percentage of rhamnose detected in its EPS repeated unit.