Comparison of the chemical structure and biological activities of the glycolipids of Salmonella minnesota R595 and Salmonella typhimurium SL1102.

It has been assumed in the past that the lipid moieties of endotoxic lipopolysaccharides are quite similar if not identical. This has been tested in the reported work here, where the chemical composition and biological activities of the glycolipids of two heptoseless Re mutants, Salmonella minnesota R595 and Salmonella typhimurium SL1102, have been studied and compared. The two glycolipids, extracted with chloroform-methanol (4:1), showed identical thin-layer chromatographic patterns. The molar ratios for hexosamine, fatty acids, phosphorus, 2-keto-3-deoxyoctonate, total amines, and total nitrogen of the purified glycolipids were in the same range, but small differences could be established. Both glycolipids contained the same major fatty acids, i.e., lauric, myristic, palmitic, and 3-hydroxymyristic acids, in similar but not identical ratios. On paper electrophoresis, the acid hydrolysates of the two glycolipids showed analogous components. In the determination of molecular weight, whereas S. minnesota R595 glycolipid did not show concentration dependence, the molecular weight measured for S. typhimurium SL1102 increased with its concentration. The molecular weight of the fully endotoxic R595 glycolipid has been found to be 17,000 +/- 1,500. Both glycolipids showed similar activities in the Shwartzman skin reaction, Limulus-lysate clotting assay, mouse lethality, and enhancement of nonspecific resistance, but the R595 preparation appeared to be more active on a weight basis in some parameters than SL1102. Using passive hemagglutination, we observed cross-reactivity between the glycolipids. In the gel-diffusion test, they revealed clear identity. The antiserum against S. minnesota R595 neutralized the Shwartzman skin reactivity not only of R595 but also of SL1102 glycolipid. These results confirm that there are identical immunodeterminant group(s) in the two glycolipids. On the other hand, chemical analytical data for two glycolipids showed only similarities, indicating that although both glycolipids are of comparable chemical nature, differences between them exist.