Abstract
Rhizobia produces different types of surface polysaccharides. Among them, cyclic β-(1→2)-d-glucan is located in the periplasmic space of rhizobia and plays an important role in the adaptation of bacteria to osmotic adaptation. Cyclic β-(1→2)-d-glucan (CG), synthesized from Sinorhiozbbium meliloti 1021, has a neutral and anionic form. In the present study, we characterized the exact chemical structures of anionic CG after purification using size exclusion s (Bio-Gel P-6 and P-2) chromatography, and DEAE-Sephadex anion exchange chromatography. The exact structure of each isolated anionic CG was characterized using various analytical methods such as nuclear magnetic resonance (NMR), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and matrix associated laser desorption ionization-time of Flight (MALDI-TOF) mass spectrometry. The precise chemical structures of novel anionic CG molecules were elucidated by various NMR spectroscopic analyses, including 1H, 13C, 31P, and 2D HSQC NMR spectroscopy. As a result, we discovered that anionic CG molecules have either glycerophosphoryl or succinyl residues at C6 positions of a neutral CG. In addition, the results of MALDI-TOF mass spectrometric analysis confirmed that there are two types of patterns for anionic CG peaks, where one type of peak was the succinylated CG (SCG) and the other was glycerophospholated CG (GCG). In addition, it was revealed that each anionic CG has one to four substituents of the succinyl group of SCG and glycerophosphoryl group of GCG, respectively. Anionic CG could have potential as a cyclic polysaccharide for drug delivery systems and a chiral separator based on the complexation with basic target molecules.
Highlights
Rhizobia are Gram-negative soil bacteria, which make Bacteroides in plants during root infection for nitrogen fixation [1]
When ethanol extracts of Sinorhizobium meliloti 1021 were chromatographed on Bio-Gel P-6 chromatography, one major peak of oligosaccharide material was detected
There have been some reports that phosphoglycerol substituents of anionic Cyclic β-(1→2)-d-glucan (CG) produced in Sinorhizobium meliloti 1021 were derived from cell membrane lipids and that this negative CG is involved in the regulation of osmotic pressure [5,17]
Summary
Rhizobia are Gram-negative soil bacteria, which make Bacteroides in plants during root infection for nitrogen fixation [1]. Rhizobium spp. produces eight different types of surface polysaccharides for nodule development such as extracellular polysaccharide (EPS), lipopolysaccharide (LPS), capsular polysaccharide (CPS), cyclic β-(1→2)-d-glucan (CG), K-antigen poly-saccharide (KPS), neutral polysaccharide (NP), gel-forming-polysaccharide (GPS) and cellulose fibrils during root nodulation [2]. Cyclic β-(1→2)-d-glucan (CG) is found in the members of Rhizobiaceae, which are fast growing soil bacteria. These molecules are a class of unbranched cyclic oligosaccharides composed of β-(1→2)-d-glucans varying in size from 17 to 26 as a major neutral or anionic form [4]. Many studies have been conducted on inclusion complexes that use neutral
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