Structural investigation of the exopolysaccharide produced by Pseudomonas flavescens strain B62 - Degradation by a fungal cellulase and isolation of the oligosaccharide repeating unit

Pseudomonas flavescens strain B62 (NCPPB 3063) is a recently described bacterium isolated from walnut blight cankers. This strain has been designated as the type strain of a Pseudomonas rRNA group-I species. Strain B62 produced a mixture of two exopolysaccharides, differing in weight average relative molecular mass and composition. Only the most abundant exopolysaccharide (90 % by mass), corresponding to the one with the lower molecular mass, was investigated by use of methylation analysis, partial acid hydrolysis, and NMR spectroscopy. The polysaccharide was depolymerised by the action of the cellulase produced by Penicillum funiculosum and the oligosaccharide obtained, corresponding to the repeating unit was characterised by NMR spectroscopy and ion-spray mass spectrometry. The repeating unit of the B62 exopolysaccharide is [GRAPHICS] where X is glucose (75 %) or mannose (25 %), and Lac is lactate. The O-acetyl groups are present only on 75 % of the repeating units, and they are linked to the C6 of the hexose residues in non-stoichiometric amounts.