Fig. 1.

M. tuberculosis catabolizes cholesterol. (A) Structure of cholesterol. The locations of the ¹⁴C label in substrates used in this study are indicated. (B) The conversion of [4-¹⁴C] or [26-¹⁴C]cholesterol to ¹⁴CO₂ by M. tuberculosis was quantified. Data are presented as the percentage of input radioactivity recovered as ¹⁴CO₂ after 4 h of culture. “Cold” indicates the addition of a 100-fold excess of unlabeled cholesterol. Error bars indicate standard deviation. (C) Cholesterol-derived carbon is assimilated into mycobacterial lipids. Bacteria were grown with cholesterol labeled at the indicated position, and the amounts of radioactivity recovered in the apolar or polar lipid extracts were determined. (D) The apolar lipid extracts of metabolically labeled bacteria were resolved by TLC. [3-¹⁴C]Propionate (Prop.) was used to specifically label branched-chain lipids such as PDIM (arrowheads). Labeled PDIM was detected in the [26-¹⁴C]cholesterol-labeled cells, but not in the [4-¹⁴C]cholesterol-labeled sample. The migration of intact cholesterol is shown (Chol.). The origin (asterisk) and direction of migration are indicated. The identity of PDIM was confirmed by purifying the species marked by arrowheads and subjecting them to atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Major ions characteristic of PDIM (45) were detected at m/z = 914, 928, 942, 956, and 970.