Cholesterol metabolism by Treponema hyodysenteriae

The sterol content of cellular lipids of Treponema hyodysenteriae, the agent of swine dysentery, was determined. When cultured in lipid-depleted brain heart infusion broth containing vesicles made from [4-14C]cholesterol and phosphatidylcholine, T. hyodysenteriae cells incorporated radioactive label. Most (95%) of this radioactivity was associated with bacterial membrane preparations. Lipids were extracted from radiolabeled cells and fractionated by silicic acid column chromatography. Components of the neutral lipid fraction were separated by reversed-phase high-performance liquid chromatography and were detected by monitoring both radioactivity and UV absorption (210 nm) of the column effluent. Cholesterol represented only about 5% of the total radioactivity in the bacterial neutral lipids. The remaining radioactivity was associated with a compound that did not absorb light at 210 nm. This lipid was purified and, on the basis of results from thin-layer chromatography and mass spectrometry, was identified as cholesterol (5 alpha-cholestan-3 beta-ol), a sterol lacking the unsaturated bond of cholesterol. Cholestanol was also present in cell-free culture broth, but only after growth of the spirochete. These results are evidence that cholesterol is used by T. hyodysenteriae for membrane synthesis. Cholesterol is converted to cholestanol in T. hyodysenteriae cultures and cholestanol is a major component (approximately 9% by weight) of T. hyodysenteriae cell lipids.