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 d esignated as the type strain of a Pseudomonas rRNA group-I species. St rain B62 produced a mixture of two exopolysaccharides, differing in we ight average relative molecular mass and composition. Only the most ab undant exopolysaccharide (90 % by mass), corresponding to the one with the lower molecular mass, was investigated by use of methylation anal ysis, partial acid hydrolysis, and NMR spectroscopy. The polysaccharid e was depolymerised by the action of the cellulase produced by Penicil lum funiculosum and the oligosaccharide obtained, corresponding to the repeating unit was characterised by NMR spectroscopy and ion-spray ma ss spectrometry. The repeating unit of the B62 exopolysaccharide is [G RAPHICS] where X is glucose (75 %) or mannose (25 %), and Lac is lacta te. The O-acetyl groups are present only on 75 % of the repeating unit s, and they are linked to the C6 of the hexose residues in non-stoichi ometric amounts.