Electron microscopic studies of endotoxins treated with alkaline and acid reagents

Endotoxins extracted from Salmonella minnesota wild strain and R mutants (Ra to Re) were treated with two different alkaline reagents. Treatment with diluted sodium hydroxide, which caused partial removal of O-ester linked fatty acids, changed the ultrastructures of endotoxins from an onion-like structure to monolayer particles (approximately 100 A in diameter) except for endotoxic glycolipids from Rd2 and Re mutants which showed mixed ultrastructures of untreated and treated endotoxins. Treatment with alkaline hydroxylamine, which caused liberation of all O-ester linked fatty acids, changed the ultrastructures of all endotoxins to monolayer particles. The results suggested that the ultrastructures of alkaline-treated endotoxins were dependent on the degree of their hydrophobicity. On the other hand, the micrographs of acid treated endotoxins did not show a constant structure because of the high hydrophobicity.