Cyclic [beta]-1,6 -1,3 Glucans Are Synthesized by Bradyrhizobium japonicum Bacteroids within Soybean (Glycine max) Root Nodules.

We have previously reported that free-living cultures of Bradyrhizobium species produce novel oligosaccharides that are cyclic, contain between 10 and 13 glucose residues, and are linked by [beta]-1,6 and [beta]-1,3 glycosidic bonds (K.J. Miller, R.S. Gore, R. Johnson, A.J. Benesi, V.N. Reinhold [1990] J Bacteriol 172: 136-142). In the present study, we show that these glucans are also synthesized by bacteroids of Bradyrhizobium japonicum USDA 110 within Glycine max root nodules.

Cell surface carbohydrates of microaerobic, nitrogenase-active, continuous cultures of Bradyrhizobium sp. strain 32H1.

A continuous culture system was developed to examine the cell surface carbohydrates of Bradyrhizobium sp. strain 32H1. When cultures were shifted from aerobic to microaerobic growth conditions, nitrogenase activity was induced and extracellular polysaccharide levels were greatly reduced; however, the levels of cell-associated cyclic beta-1,6 -1,3 glucans were found to be essentially unchanged.

Diglyceride Kinase Activity in Cell Extracts of Rhizobium meliloti: Evidence for a Diglyceride Cycle during Cyclic beta-1,2-Glucan Biosynthesis.

In this article, we provide evidence for the presence of diglyceride kinase activity in cell extracts of Rhizobium meliloti 1021. Characterization of the rhizobial enzyme revealed that it shares many properties with the diglyceride kinase of Escherichia coli. A possible role for this enzyme during cyclic beta-1,2-glucan biosynthesis is discussed.

Cell-associated oligosaccharides of Bradyrhizobium spp.

We report the initial characterization of the cell-associated oligosaccharides produced by four Bradyrhizobium strains: Bradyrhizobium japonicum 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.

Phosphoglycerol substituents present on the cyclic beta-1,2-glucans of Rhizobium meliloti 1021 are derived from phosphatidylglycerol.

The synthesis of periplasmic cyclic beta-1,2-glucans is a property unique to species of the family Rhizobiaceae. For this reason, it is generally believed that these molecules may play an important role in the plant infection process. In the present study, we determined that the cyclic beta-1,2-glucans produced by Rhizobium meliloti 1021 were predominantly anionic in character and contained both phosphoglycerol and succinic acid substituents. In addition, we demonstrated that phosphatidylglycerol was the source of the phosphoglycerol substituents present on these oligosaccharides and that greater than 60% of the total phospholipid turnover in this organism involved this substitution reaction.