title: Structural characterization of an acidic exoheteropolysaccharide produced by the nitrogen-fixing bacterium Burkholderia tropica.
abstract: 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.
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, 81.531-990 Curitiba, PR, Brazil.
authors.forename: Rodrigo V
authors.initials: RV
authors.lastname: Serrato
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, 81.531-990 Curitiba, PR, Brazil.
authors.forename: Guilherme L
authors.initials: GL
authors.lastname: Sassaki
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, 81.531-990 Curitiba, PR, Brazil.
authors.forename: Philip A J
authors.initials: PA
authors.lastname: Gorin
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, 81.531-990 Curitiba, PR, Brazil.
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Cruz
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, 81.531-990 Curitiba, PR, Brazil.
authors.forename: Fábio O
authors.initials: FO
authors.lastname: Pedrosa
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, United States.
authors.forename: Biswa
authors.initials: B
authors.lastname: Choudhury
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, United States.
authors.forename: Russell W
authors.initials: RW
authors.lastname: Carlson
authors.affiliation: Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná, 81.531-990 Curitiba, PR, Brazil. Electronic address: iacomini@ufpr.br.
authors.forename: Marcello
authors.initials: M
authors.lastname: Iacomini
keywords: Burkholderia; Diazotrophic; EPS; Endophytic; Exopolysaccharide