Lipid on capsular polysaccharides of gram-negative bacteria

Hydrolysis of the meningococcal group A, B, and C, and Escherichia coli K92 polysaccharides by 60% aqueous hydrofluoric acid liberated various 1,2-diacylglycerols. These were extracted with chloroform, trimethylsilylated, and analyzed by gas chromatography-mass spectrometry. Two 1,2-diacylglycerols were the major components isolated. In each polysaccharide, 80 to 90% dipalmitoyl glycerol and 10 to 20% distearoyl glycerol were identified. No monoacylglycerols or mixed diacylglycerols were noted. The presence of the hydrophobic end causes the polysaccharides to aggregate in a micellar form and may be the entity by which the polysaccharide remains attached to the outer membrane of the bacterium giving rise to the structure recognized as a capsule.