Structural elucidation and biological studies of a novel exopolysaccaride from Klebsiella pneumoniae PB12

An exopolysaccharide (KNPS) of an average molecular weight ∼1.8 × 105 Da was isolated from the culture medium of Klebsiella pneumoniae PB12. Structural characterization of KNPS was carried out using sugar and methylation analysis, Smith degradation and 1D/2D NMR experiments. Sugar analysis showed that the KNPS composed of arabinose, galactose, 3-O-methyl-galctose and glucose in a molar ratio of nearly 4:3:1:1. The proposed repeating unit of the KNPS has a backbone chain consisting of two (1 → 6)-galactopyranosyl residues, two (1 → 5)-arabinofuranosyl residues, one (1 → 6)-glucopyranosyl residue and one (1 → 3)-arabinopyranosyl residue, out of which one (1 → 6)-galactopyranosyl residue was branched at O-2 position with a (1 → 2)-linked-galactopyranosyl residue terminated with non reducing arabinofuranosyl residue and one (1 → 5)-arabinofuranosyl residue branched at O-3 position with non reducing end 3-O-Me-galactopyranosyl residue. KNPS was found non-toxic toward human lymphocyte up to the dosage of 100 μg/ml. KNPS enhanced malondialdehyde (MDA), reactive oxygen species (ROS), and have the potential to alter the ratio of oxidized glutathione (GSSG) and reduced glutathione (GSH) levels in the cellular system.