Degree Name

Master of Science (MS)

Semester of Degree Completion

1983

Thesis Director

Russell Carlson

Abstract

The Rhizobium trifolii polysaccharides from SU843 and mutants--HC843(pBR1AN), HC843, 8002--in which the sym plasmid is replaced, absent, or mutated by transposon Tn5 were isolated. The surface polysaccharides of genetically altered mutants were compared quantitatively and qualitatively with one another and with the parent strain. The interpretation of these results is discussed in relation to the function of Rhizobium surface polysaccharides in the symbiotic process. The symbiotic ability of SU843 and mutant strains is as follows: (a) SU843, nod+, fix+; (b) mutant 8002, roa+ (still attaches to root hair), hac-, nod-; (c) mutant HC843, roa+, hac-, nod-; (d) mutant HC843(pBR1AN), nod+, fix+. In addition to EPS (extra-cellular polysaccharide), CPS (capsular polysaccharide), and LPS (lipopolysaccharide), we found a polysaccharide "slime", which is a viscous material removed from the viscous bacterial pellet by fresh media. Comparing these polysaccharides, we found that the nod+ strains--SU843 and HC843(pBR1AN)--contain both CPS and slime polysaccharides. But the nod- strains--HC843 and 8002--are absent at one or the other polysaccharides (CPS, slime). This suggests that there exists a sym plasmid-influenced enzyme which controls the EPS to adhere to and to aggregate around the cell membrane and is important to the symbiotic process.

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