Degree Name

Master of Science (MS)

Semester of Degree Completion

1984

Thesis Director

Russell Carlson

Abstract

The fast-growing strains of R. japonicum were originally isolated from China. They are acid-producing Rhizobia and are capable of nodulating soybeans. These isolates share a common host-specificity (Peking soybean) with the slow-growing R. japonicum strains even though their biochemical properties are more closely related to other fast-growing Rhizobium species. The surface polysaccharides from three fast-growing R. japonicum strains--USDA201, USDA205, and HC205--were isolated and partially characterized. Strain HC205 is a nod⁻ mutant of USDA205 which lacks the symbiotic plasmid. These surface polysaccharides consist of extracellular, capsular and lipopolysaccharides (EPSs, CPSs and LPSs). The EPSs from all three strains are very similar in composition having galactose, glucose, uronic acid and acetate. These components are similar to the EPSs from other fast-growing Rhizobium species except for pyruvate which is not detected in the EPSs from fast-growing R. japonicum strains. The CPSs from USDA205 and HC205 are very similar to the EPSs in composition except they contain increased amounts of acetate. The CPS from USDA201 is isolated in very small amounts and is different in composition from the EPSs in that it is reduced in glucose and increased in uronic acid. The EPSs and CPSs are different from those of the slow-growing R. japonicum strains which vary from strain to strain and can consist of methylated sugars and deoxysugars. The LPSs were purified by phenol/water extraction and gel filtration chromatography. The LPSs from USDA205 and HC205 elute as broad peaks from the gel filtration column and contain 2-keto-3-deoxyoctonic acid (KDO) as one of the major sugar components. The LPS from HC205 differs from that of USDA205 in that it contains ribose. Both USDA205 and HC205 LPSs have a lamba max at 260 nm. Both the ribose content and the lamba max at 260 nm are resistant to RNase treatment. Gel-filtration of the phenol/water extracted polysaccharides from USDA201 results in two distinct KDO containing peaks (LPS1 and LPS2). Both LPS1 and LPS2 have similar compositions containing ribose, 2,3-di-O-methyl-hexose, galactose, glucose and KDO. Again KDO is a major sugar, LPS2 having the largest amount of KDO. None of the LPSs contain heptose. The presence of KDO as a major sugar in the LPSs makes these LPS different from the phenol/water extracted polysaccharides of the slow-growing R. japonicum strains which do not contain detectable levels of KDO, and different from the LPSs from other fast-growing Rhizobium species which contain 1-5% KDO. The LPSs from R. meliloti strains are other LPSs in which KDO is a major sugar. Polyacrylamide gel electrophoresis shows that the LPS are typically heterogeneous molecules. Differences in banding patterns are observed among the fast-growing R. japonicum LPSs as well as the differences between these LPSs and other fast-growing Rhizobium LPSs.

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