Structure of an acidic exopolysaccharide produced by the diazotrophic endophytic bacterium Burkholderia brasiliensis

The structure of an exopolysaccharide (EPS) produced by Burkholderia brasiliensis, a diazotrophic endophytic organism originally isolated from rice roots, has been determined. The bacterium was grown in a synthetic medium, containing mannitol and glutamate, which favours the expression of two anionic EPSs, which were separated by anion-exchange chromatography. The structure of the repeat unit of EPS A, eluted at higher ionic strength, was determined by a combination of methylation analysis, partial hydrolysis, chemical degradations, and NMR spectroscopic studies, and shown to be the linear O-acetylated pentasaccharide: -->4)-alpha -D-Glcp-( 1 -->2)-alpha -L-Rhap-( 1 -->4)-alpha -D-GlcpA-( 1 -->3)beta -L-Rhap[20Ac]-(1 -->4)-beta -D-Glcp-(1 -->.