Cell Surface Carbohydrates of Microaerobic , Nitrogenase - Active , Continuous Cultures of Bradyrhizobium sp . Strain 32 H 1 RICHARD S . GORE ' AND KAREN

  • J . MILLER


Members of the genera Rhizobium and Bradyrhizobium are distinguished from other species by their ability to infect leguminous plants. This infection process leads to the development of nitrogen-fixing nodules on the roots of the legume host. Within these nodules, the bacteria are released intracellularly and differentiate into nitrogen-fixing forms termed "bacteroids." The cell surface carbohydrates of these bacteria are believed to provide functions during the plant infection process. These carbohydrates include extracellular polysaccharides, capsular polysaccharides, lipopolysaccharides, and oligosaccharides. Studies in our laboratory have focused upon a class of rhizobial oligosaccharides, the cyclic beta glucans, and we have shown that the cyclic beta glucans of bradyrhizobial species are different in structure than those synthesized by Rhizobium species. Specifically, the cyclic beta glucans produced by Rhizobium species contain 17 to 24 glucose residues linked solely by beta-1,2 glycosidic linkages, while the bradyrhizobial cyclic beta glucans are smaller (10 to 13 glucose residues) and are linked by both beta-1,6 and beta-1,3 glycosidic linkages (6, 7). The differentiation of bacterium to bacteroid has been found to be associated with numerous changes in cell metabolism, a general increase in cel volume, and an alteration in cell surface carbohydrate composition. With regard to cell surface carbohydrate composition, it appears that biosynthesis of extracellular polysaccharide, capsular polysaccharide, and lipopolysaccharide is greatly reduced in the bacteroid state (2, 4, 8, 10-12, 14, 15), suggesting, perhaps, that these cell surface carbohydrates provide functions primarily during the early stages of legume nodulation. In order to gain a further understanding of the cell surface carbohydrate changes which occur during bacteroid differentiation, we have taken advantage of the fact that strains of Bradyrhizobium are capable of bacteroid differentiation ex planta during microaerobic growth. In the present study, we have utilized a continuous culture system to examine the effects of microaerobic growth conditions on the biosynthesis of cellassociated cyclic beta-1,6 -1,3 glucans by Bradyrhizobium sp. strain 32H1. Continuous culture conditions. Bradyrhizobium sp. strain 32H1 has been previously described (7). Cells were grown in

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@inproceedings{MILLERCellSC, title={Cell Surface Carbohydrates of Microaerobic , Nitrogenase - Active , Continuous Cultures of Bradyrhizobium sp . Strain 32 H 1 RICHARD S . GORE ' AND KAREN}, author={J . MILLER} }