Table 1.

Phospholipids and cholesterol in the cell membrane of representative Mycoplasma species.

Mycoplasma species	PL	C	CE	C/PL (molar ratio)	Reference
	(nmole/mg membrane protein)
M. hyorhinis	205.0	235.3	51.7	1.15	—
M. penetrans	125.5	157.1	22.3	1.25	[12]
M. fermentans	203.5	150.0	50.0	0.99	[13]
M. gallisepticum	167.0	76.0	4.7	0.48	[14]
M. capricolum	227.0	75.0	72.3	0.64	[15]

M. hyorhinis was grown in a modified Hayflick's medium [16] to the mid-exponential phase of growth, and isolated membranes were prepared as previously described [17]. Lipids were extracted from membrane preparations by the method of Bligh and Dyer [18]. Unesterified cholesterol, cholesterol esters, and phospholipids were separated on Merck Silica Gel G glass plates using benzene : diethyl ether : ethanol : acetic acid (50 : 40 : 2 : 0.2). The unesterified cholesterol and the cholesterol esters spots were extracted with chloroform for 30 min at room temperature, and the sterol content was determined by the phthaldialdehyde method [19]. Phosphorus in the phospholipid spot was determined by the method of Zhou and Arthur [20] using KH₂PO₄ as a standard. In brief, the spots were scraped from the plate into test tubes, digested with 0.5 mL of 70% perchloric acid (HClO₄), and transferred into a 2 mL solution containing malachite green (0.2%) and ammonium molybdate (4%) in Tween-20 (1.5% w/v) and 5 M HCl (3 : 1 by vol.). The results are the average of three independent experiments using different batches of cells. PL: total phospholipids; TC: total cholesterol; C: unesterified cholesterol; CE: cholesterol esters.