Cell-associated oligosaccharides of Bradyrhizobium spp

Abstract

We report the initial characterization of the cell-associated oligosaccharides produced by four Bradyrhizobium strains: Bradyrhizobiumjaponicum USDA 110, USDA 94, and ATCC 10324 and Bradyrhizobium sp. strain 32H1. The cell-associated oligosaccharides of these strains were found to be composed solely of glucose and were predominantly smaller than the cyclic beta-1,2-glucans produced by Agrobacterium and Rhizobium species. Linkage studies and nuclear magnetic resonance analyses demonstrated that the bradyrhizobial glucans are linked primarily by beta-1,6 and beta-1,3 glycosidic bonds. Thus, the bradyrhizobia appear to synthesize cell-associated oligosaccharides of structural character substantially different from that of the cyclic beta-1,2-glucans produced by Agrobacterium and Rhizobium species.Bacterial genera in the family Rhizobiaceae are distinguished by their ability to infect higher plants. In the case of Rhizobium and Bradyrhizobium species, this infection process leads to a beneficial symbiotic relationship in which nitrogen-fixing nodules develop on the roots of leguminous plants. Plant infection by Agrobacterium species, however, results in the production of tumors on susceptible plant hosts. The cell surface carbohydrates of all three genera are believed to play important roles in the plant infection process. These cell surface carbohydrates include extracellular polysaccharides, capsular polysaccharides, lipopolysaccharides, and periplasmic glucans. Recent studies have demonstrated that Agrobacterium and Rhizobium species synthesize neutral and anionic periplasmic glucans of similar structure (2,5,16,17,20,21,23). In both genera, these periplasmic glucans are composed of a cyclic beta-1,2-glucan backbone containing 17 to 24 glucose residues. In Agrobacterium tumefaciens, approximately 50% of the total periplasmic cyclic beta-1,2-glucans are present as neutral, unsubstituted molecules (22). The remaining molecules are substituted with one or more phosphoglycerol moieties (23). In Rhizobium meliloti, as much as 90% of the periplasmic cyclic beta-1,2-glucans may be substituted with anionic moieties (21). As in the cyclic glucans of A. tumefaciens, the predominant anionic substituent present on the cyclic beta-1,2-glucans of R. meliloti 1021 is phosphoglycerol (21).Recently, studies by Nester and co-workers (9, 26) and Geremia and co-workers (11) have provided evidence for a role for cyclic beta-1,2-glucans in the plant infection process. Specifically, cyclic beta-1,2-glucans have been implicated in the attachment of the bacterial cell to the plant host. Although there have been previous reports that at least two strains of Bradyrhizobium japonicum are capable of synthesizing neutral beta-1,2-linked glucans (1, 4), very little characterization of the cell-associated oligosaccharides of Bradyrhizobium species has been performed to date. We now report the results of our analyses of the cell-associated oligosaccharides of four Bradyrhizobium strains.(A preliminary report of this work has appeared previ-* Cor...

Synthesis of glycerophosphorylated cyclic (1,2)- -glucans in Rhizobium meliloti strain 1021 after osmotic shock

“…Further analysis by gel permeation and ion-exchange chromatography revealed that anionic 3H-labelled cyclic (1,2)-Pglucans represented 2 93% of the radiolabel present within these extracts. In a previous study, similar results were reported, and it was shown that [3H]phosphoglycerol (derived from the head group of phosphatidylglycerol) accounted for all of the radiolabel associated with the 3H-labelled cyclic (1,2)$-glucan fraction (Miller et al, 1988).…”

“…In some experiments, chloramphenicol(lO0 pg ml-l) was added to cultures at the beginning of the chase period. At various times during the chase period, cultures were centrifuged, and radiolabelled cyclic (1,2)-p-glucans were extracted from cell pellets into aqueous methanol (Miller et a/., 1988). Radiolabelled cyclic glucans were analysed by gel permeation and ion-exchange column chromatography as previously described .…”

Periplasmic glucans of Pseudomonas syringae pv. syringae

“…Periplasmic glucans of Bradyrhizobium spp. are predominantly neutral (25), but Rolin and coworkers (34) have purified phosphocholine-substituted 13-1,6-and 1-1,3-glucans from Bradyrhizobium japonicum USDA 110.…”

“…Extracts of Bradyrhizobium spp. revealed the presence of P-1,6-and 3-1,3 cyclic glucans containing 10 to 13 glucose units per ring (25). Periplasmic glucans of E. coli, also known as MDOs (membrane-derived oligosaccharides), appear to range from 6 to 12 glucose residues, with the principal species containing 8 or 9 glucose residues (13).…”

Structure and Ethanol Complexation of Cyclic Tetrasaccharide in Aqueous Solution Studied by NMR and Molecular Mechanics

“…The complex that has i ethanol molecules at the site A and j ethanol molecules at the site will be denoted as CTSA i B j , where i and j, respectively, are 0, 1, and 2. This complex can be formed stepwise as 21,22) CTSA iϪ1 B j ϩETϭCTSA i B j (4) and…”