Degree Name

Master of Science (MS)

Semester of Degree Completion

1984

Thesis Director

Kandy D. Baumgardner

Abstract

Extracellular polysaccharides (EPS) and lipopolysaccharides (LPS) are suspected to be involved in the legume/Rhizobium symbiotic process. Polysaccharide compositions from the EPS, LPS, capsular polysaccharide (CPS), and small polysaccharide (SmPS) were compared between Rhizobium leguminosarum ANU57 (parent, Exo-1) and two mutants R. leg. ANU57(pBR1AN) (nod+, nif-) and R. leg. ANU57(pJB5J1) (nod+, nif-) both containing a Sym (symbiotic) plasmid insertion. R. leg. ANU57(pBR1AN) and R. leg. ANU57(pJB5J1) are nod+ on clover and peas, respectively. The nod+ mutants produce larger amounts of EPS and decreased amounts of LPS compared to the parental strain. However, the EPS found in these nod+ mutants do not have the same EPS content found in the original R. leg. 128c53 Exo+1, nod+1, nif+1 parent, and thus do not support a role for EPS in the early steps of symbiosis. Pyruvate was present in the EPS of the mutant strains but not in the parental EPS. Pyruvate was found in the LPS of all three strains suggesting a Sym plasmid insertion of a possible modifying enzyme function (e.g., pyruvate linking) in the nod+ mutants. The uronic acid content in the EPS (Pk. II) of the mutant R. leg. ANU57(pJB5J1) is three times the amount found in the EPS (Pk. II) of the parent. R. leg. ANU57(pBR1AN) showed no distinguishable separation into EPS (Pk. I) and EPS (Pk. II) fractions, and thus the possible significance of this uronic acid difference requires further investigation. Sugar compositions of the parent and two mutant strains indicate an LPS component in the EPS. The relative mole percent composition of rhamnose, fucose, mannose, galactose, and KDO for the EPS, LPS, and CPS of the parent are similar to the corresponding EPS, LPS, and CPS of the two mutant strains. The possible effects these differences may have on legume/Rhizobium symbiosis are discussed.

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