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Structural characterization of an acidic exoheteropolysaccharide produced by the nitrogen-fixing bacterium Burkholderia tropica
- Serrato, R.V., Sassaki, G.L., Gorin, P.A.J., Cruz, L.M., Pedrosa, F.O., Choudhury, B., Carlson, R.W., Iacomini, M.
- Carbohydrate polymers 2008 v.73 no.4 pp. 564-572
- Burkholderia, biopolymers, chemical structure, polysaccharides, soil bacteria, nitrogen-fixing bacteria
- An acidic exopolysaccharide (EPS) produced by the diazotrophic bacterium Burkholderia tropica, strain Ppe8, was isolated from the culture supernatant of bacteria grown in a synthetic liquid medium containing mannitol and glutamate. Monosaccharide composition showed Rha, Glc and GlcA in a 2.0:2.0:1.0 molar ratio, respectively. Further structural characterization was performed by a combination of NMR, mass spectrometry and chemical methods. Partial acid hydrolysis of EPS provided a mixture of acidic oligosaccharides that were characterized by ESI-MS, giving rise to ions with m/z 193 (GlcA-H)-, 339 (GlcA,Rha-H)-, 501 (GlcA,Rha,Glc-H)-, 647 (GlcA,Rha2,Glc,-H)-, 809 (GlcA,Rha2,Glc2,-H)- and 851 (GlcA,Rha2,Glc2,OAc-H)-. Carboxyreduced EPS (EPS-CR) had Glc and Rha in a 3:2 ratio, present as d- and l-enantiomers, respectively. Methylation and NMR analysis of EPS and EPS-CR showed a main chain containing 2,4-di-O-Rhap, 3-O-Rhap and 4-O-Glcp. A GlcA side chain unit was found in the acidic EPS, substituting O-4 of α-l-Rhap units. This was observed as a non-reducing end unit of glucopyranose in the EPS-CR. Acetyl esters occured at O-2 of β-l-Rhap units. From the combined results herein, we determined the structure of the exocellular polysaccharide produced by B. tropica, Ppe8, as being a pentasaccharide repeating unit as shown: (...)