The Steroid Growth-Requirement of Mycoplasma mycoides

SUMMARY: Several steroids closely related structurally to cholesterol were tested for growth-promoting activity for a strain of Mycoplasma mycoides (V5) and a Mycoplasma sp. isolated from a goat (gy). Cholestanol and latho-sterol promoted growth of both strains. Cholestenone, cholest-5-en-3-one, 7-dehydrocholesterol and progesterone inhibited cholesterol-promoted growth; cholestanone was almost inactive either as growth promotor or as growth inhibitor. Cholesterol amounted to 4–5% of the dry weight of the water-washed organisms, or about 20% of the total lipids, of either strain grown in the presence of cholesterol. Cholesterol esters or transformations to other steroids were not detected in lipid extracts of the v5 strain grown in the presence of cholesterol-4-14C. The gy strain was grown in the presence of cholesterol-4-14C of known specific activity, the lipid extract diluted with a known amount of unlabelled cholesterol, and cholesterol isolated and purified. Its specific activity was very close to the value expected if no sterol transformations had occurred. When grown in the presence of cholestanol, the gy strain incorporated this sterol without desaturation.