Liquid chromatography-mass spectrometry analysis of major lipid species in Bacteroides thetaiotaomicron VPI 5482

Bacteroides thetaiotaomicron colonizes the human gastrointestinal tract and establishes a symbiotic relationship with the host, contributing to reducing intestinal inflammation and enhancing resistance against foreign pathogens. Recent reports have revealed that diverse lipid species such as glycerophospholipids, sphingolipids, and N-acyl amines exist in B. thetaiotaomicron and play essential roles in the immune process. In this research, total lipids obtained from B. thetaiotaomicron were purified via thin-layer chromatography, and the species and molecular structures of visible lipids in different hydrophobic regions were qualitatively characterized by high-performance liquid chromatography-mass spectrometry. The results indicated that seven lipid species were primarily displayed on the plate, including phosphatidylethanolamine, ethanolamine phosphoryl dihydroceramide, inositol phosphoryl dihydroceramide, glycyl-serine phosphoryl dihydroceramide, phosphatidylglycerol, cardiolipin, and glycyl-serine phosphoryl diacylglycerol. The phosphatidylethanolamine, ethanolamine phosphoryl dihydroceramide, and inositol phosphoryl dihydroceramide species corresponding to ion peaks at m/z 676.48, 691.53, and 796.53 exhibited significantly high abundance compared to other species, suggesting their prevalent presence in total lipids. The molecular structures of phosphatidylethanolamine and ethanolamine phosphoryl dihydroceramide were derived from the modification of diacylglycerol and dihydroceramide with phosphoethanolamine, while the structure of inositol phosphoryl dihydroceramide was derived from the modification of dihydroceramide with phosphoinositol. The phosphatidylglycerol and cardiolipin species corresponding to m/z 721.51 and 1323.94 have been detected in the membrane lipids of B. thetaiotaomicron, although they were not mentioned in previous studies. These findings are important for understanding the molecular mechanisms of B. thetaiotaomicron colonization in mammalian gut.