Master of Science (MS)
Semester of Degree Completion
The surface polysaccharides of Rhizobium are implicated in the symbiotic process. The composition of the surface polysaccharides from two strains of Rhizobium japonicum, I110 ARS and 61A76 str, have been compared. Five polysaccharide fractions are obtained from the I110 ARS strain. They are the EPS (extracellular polysaccharide), CPS-1 and CPS-2 (capsular polysaccharide fractions), LPS (lipopolysaccharide) and Phe (polysaccharide found in the phenol layer from the phenol/water extraction). These polysaccharide fractions have identical sugar compositions. Four polysaccharide fractions are obtained from the 61A76 str strain. These are the EPS, CPS-1, SmPS (small molecular weight polysaccharide), and Phe. Each of these polysaccharide fractions has a different sugar composition. The 61A76 str strain does not have a CPS-2 or an LPS fraction. These results show that the I110 ARS and 61A76 str strains are not closely related in their surface polysaccharides. However, one similarity is found between the two strains. The compositions of the CPS-1 fractions from both strains are qualitatively similar. This similarity may explain why both strains are able to infect soybean plants. Neither of the R. japonicum strains appears to have a typical LPS. The I110 ARS strain possesses an LPS fraction, however, upon analysis it was found that it contained a very low amount, 0.02%, of KDO and it is not affected by mild acid treatment. In a normal LPS, KDO makes up 3-5% of the total mass and treatment with a mild acid causes hydrolysis of the bond between the lipid and the polysaccharide. The 61A76 str. strain does not possess a polysaccharide fraction which elutes from a Sepharose 48 column where a typical LPS elutes.
These surface polysaccharides may interact with proteins on the surface of the soybean root. Attempts were also made at isolating these protein molecules using root protein fractions and an EPS-acrylamide affinity column. About 9% of two protein fractions, the surface and membrane proteins, was found to bind to the column. Attempts to release the bound material proved to be ineffective. All of these results are discussed with regard to their role in the R. japonicum-soybean symbiosis.
Koehler, Richard F., "A Comparison of the Surface Polysaccharides from Rhizobium japonicum strains I110ARS and 61A76str, and the Isolation of Soybean Root Proteins Responsible for the Binding of EPS from R. japonicum strain I110ARS" (1982). Masters Theses. 2920.