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.
MALDI-TOF, Bradyrhizobium, cyclic-b-glucan, osmoregulation, Phosphocholinyl and succinyl substituents
NCBI PubMed ID: 21665197Publication DOI: 10.1016/j.carres.2011.05.015Journal NLM ID: 0043535Publisher: Elsevier
Correspondence: A. Choma
; achoma@hektor.umcs.lublin.pl
Institutions: Department of Genetics and Microbiology, Maria Curie-Sklodowska University, 19 Akademicka St., 20-033 Lublin, Poland
Methods: 13C NMR, 1H NMR, methylation, NMR-2D, GC-MS, HF solvolysis, de-O-acylation, MALDI-TOF MS, composition analysis, NMR-1D
Found