Sphingolipid metabolism in Bacteroideaceae.

The lipid composition of the anaerobic Bacteroides thetaiotaomikron has been analyzed. Sphingomyelin, ceramide phosphinicoethanolamine, free even-numbered and branched chain sphingosine bases and ceramide represented about 50% of the total lipid extract. The main ester phospholipid was phosphatidylethanolamine. The alkali-stable sphingophospholipids were predominantly N-acylated with 3-hydroxypalmitic acid, whereas the ester phospholipids are preferentially substituted with normal even and odd-numbered and branched-chain fatty acids. When Bacteroides was grown in a medium supplemented with labelled palmitic acid, this fatty acid was utilized for acylation reactions and to a large extent for the de novo synthesis of sphinganine. This long-chain base was incorporated into the sphingolipids and was also present in free form. The 3-hydroxypalmitic acid present in sphingolipids is not derived from palmitic acid, since labelled palmitate did not serve as a precursor. Free sphinganine added to the culture medium was also utilized efficiently for the biosynthesis of the sphingolipids by growing Bacteroides cultures. The 3H/14C ratio in sphingomyelin and ceramide phosphinicoethanolamine is the same, when [1-14C]palmitic acid and [3-3H]sphinganine serve as precursors. Sphingomyelin, which is usually only present in higher animals, is synthesized de novo in this Bacteroides strain.