title: Characterization of cyclic β-glucans of Bradyrhizobium by MALDI-TOF mass spectrometry.
abstract: Periplasmic, cyclic β-glucans isolated from Bradyrhizobium elkanii, Bradyrhizobium liaoningense, and Bradyrhizobium yuanmingense strains have been investigated by means of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS), 1D and 2D nuclear magnetic resonance (NMR), as well as standard chemical methods. These compounds are built of 10-13 d-glucose residues. The main fractions contain molecules assembled of 12 hexose units (M(w)=1945.363Da). Glucose monomers are linked by β-(1→3) or β-(1→6) glycosidic bonds. The ratio of β-(1→3) to β-(1→6) linked glucose is approximately 1:2. Moreover, methylation analysis demonstrated the presence of terminal, non-reducing, as well as branched (i.e., 3- and 6-substituted) glucoses. Thus, the basic structure of the investigated compounds is similar to that of periplasmic oligosaccharides from Bradyrhizobium japonicum and Azorhizobium caulinodans strains. The analyzed cyclic β-glucans are substituted by phosphocholine (PC) (one or two residues per ring) and highly decorated with acetate and succinate. The substituents are arranged diversely in the population of cyclic β-glucan molecules. The concentrations of cyclic β-glucans in Bradyrhizobium periplasmic space are osmotically regulated and increase in response to a decrease of medium osmolarity.
authors.affiliation: Department of Genetics and Microbiology, Maria Curie-Sklodowska University, Lublin, Poland. adam.choma@poczta.umcs.lublin.pl
authors.forename: Adam
authors.initials: A
authors.lastname: Choma
authors.forename: Iwona
authors.initials: I
authors.lastname: Komaniecka
mesh_terms: D020369:Bradyrhizobium / Q000737:chemistry*; D002240:Carbohydrate Sequence; D008401:Gas Chromatography-Mass Spectrometry; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D047071:beta-Glucans / Q000737:chemistry*
chemical_list: D047071:beta-Glucans