title: Structural characterisation of lipo-chitin oligosaccharides isolated from Bradyrhizobium aspalati, microsymbionts of commercially important South African legumes.
abstract: The shoots of the South African legume Aspalathus linearis spp. linearis (A. linearis) are used in the manufacture of an increasingly popular beverage that has acclaimed beneficial effects on health; this important export product is known as Rooibos (or Redbush) tea. Three strains of Bradyrhizobium aspalati, which are the nitrogen-fixing symbionts of Aspalathus carnosa, A. hispida and A. linearis, were tested for the production of lipo-chitin oligosaccharide signal molecules using thin-layer chromatographic analysis after induction with different inducers, including Rooibos tea extract, and radioactive labelling. Large-scale separation, using high-performance liquid chromatography, of lipo-chitin oligosaccharides from B. aspalati isolated from A. carnosa was performed for structural characterisation using fast-atom bombardment mass spectrometry and chemical modifications followed by gas chromatography-mass spectrometric analysis. The strain was shown to secrete a family of unusual lipo-chitin oligosaccharides that are highly substituted on the nonreducing-terminal residue but unsubstituted on the reducing-terminal residue. They have a backbone of three to five beta-(1-->4)-linked N-acetyl-D-glucosamine residues substituted on the nonreducing terminus with a C16:0, C16:1, C18:0, C18:1, C19:1cy, or C20:1 fatty acyl chain, and are both N-methylated and 4,6-dicarbamoylated.
authors.affiliation: Department of Mass Spectrometry, Bijvoet Center for Biomolecular Research, Utrecht University, The Netherlands.
authors.forename: C M
authors.initials: CM
authors.lastname: Boone
authors.forename: M M
authors.initials: MM
authors.lastname: Olsthoorn
authors.forename: F D
authors.initials: FD
authors.lastname: Dakora
authors.forename: H P
authors.initials: HP
authors.lastname: Spaink
authors.forename: J E
authors.initials: JE
authors.lastname: Thomas-Oates
mesh_terms: D020369:Bradyrhizobium / Q000737:chemistry / Q000502:physiology*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002686:Chitin / Q000737:chemistry / Q000302:isolation & purification; D007887:Fabaceae / Q000382:microbiology* / Q000502:physiology; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D010946:Plants, Medicinal; D013019:South Africa; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013559:Symbiosis
chemical_list: D008070:Lipopolysaccharides; C023023:lipid-linked oligosaccharides; D002686:Chitin