Degree Name

Master of Science (MS)

Semester of Degree Completion

1982

Thesis Director

Russell Carlson

Abstract

Bacteria of the genus Rhizobium are capable of forming a complex nitrogen fixing (fix+) symbiotic association with leguminous plants. The surface polysaccharides are believed to be essential in the symbiotic process. The surface polysaccharides of a genetically altered Rhizobium trifolii mutant, 8002--which does not cause root hair curling (HAC-), forms no nodules (Nod-) nor fixes nitrogen (Fix-)--is compared with its parent, SU843, which causes root hair curling (HAC+), forms nodules (Nod+), and fixes nitrogen (Fix+). Three types of surface polysaccharides--extracellular polysaccharide(s) (EPS), capsular polysaccharide(s) (CPS), and lipopolysaccharide(s) (LPS)--were obtained for each bacterial strain. Both bacterial strains produce EPS, which are very similar in composition. The mutant, 8002, produces a CPS which is 1/38 the amount produced by the parent, SU843. The 8002 CPS contains the sugars 2-0-methyl-6-deoxyhexose, rhamnose, and 2-keto-3-deoxyoctonic acid, whereas the parent CPS does not contain these sugars. The LPS of both bacterial strains are similar in sugar composition. The amount of SU843 LPS is five times greater than the amount of the mutant, 8002, LPS. The sugar composition of the O-antigens from both bacterial strains are similar, whereas the sugar compositions of their cores differ quantitatively. The small molecular weight polysaccharide(s) (SmPS) of both bacterial strains are different in sugar composition. The interpretation of these results is discussed in relation to the functions of the Rhizobium surface polysaccharides in the symbiotic process.

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