C. A. Wilham

Heterogeneity in dextran preparations

Abstract 1. 1. Three types of heterogeneity have been demonstrated in the polysaccharide products from many dextran-producing bacteria. These are gross heterogeneity in the culture, and both size and structural heterogeneity in the major fermentation product, dextran. 2. 2. Molecular size, physically and/or chemically bound impurities, or chemically bound fructose were responsible for the gross differences between the minor components of the dextran culture and the major component, dextran. 3. 3. Structural heterogeneity appears to be a normal occurrence in dextrans. The frequency and extent to which this heterogeneity occurs increases with the percentage of non-1,6-linked units. 4. 4. Analytical and preparative fractional precipitation methods have been established for studying the heterogeneity in dextrans. Application of these methods to five typical dextrans permits a tentative interpretation of the extent and nature of the heterogeneity in dextran preparations from many different bacterial strains. 5. 5. Information on the heterogeneity of the dextran component itself is essential for the characterization and utilization of dextrans. 6. 6. Examination of dextran products derived from progeny of individual cells of two strains which produce heterogeneous dextrans has failed to show the presence of mutant or variant cells.

Properties of dextrans isolated from whole cultures at various stages of incubation.

Abstract 1. 1. The decrease in viscosity which dextran from Leuc. mesenteroides NRRL B-512 exhibits when left in the culture fluid after synthesis is complete was shown to result from partial degradation to smaller macromolecular size. 2. 2. Other dextrans representing a diversity of structures from three species were shown to remain unchanged in cultures as long as 49 days. 3. 3. Length of incubation appeared not to influence the presence in cultures of two strains studied of polysaccharide products separable from the dextran component on the basis of solubility. 4. 4. Leuc. dextranicum NRRL B-1146 produces a dextran closely comparable in structure to that from the B-512 strain, but which is not degraded in the culture fluid. The only polysaccharide produced by this strain is dextran; in contrast to the B-512 strain, it produces no 50–65% ethanol-insolubles. 5. 5. Dextrans isolated prior to and at the time of complete fermentation showed differences so small as to be of questionable structural significance.