1. Total lipid was extracted from Mycoplasma laidlawii strain B with chloroform-methanol mixtures and fractionated into neutral lipid, glycolipid and phospholipid components by chromatography on silicic acid. 2. Saponification of the glycolipid fraction, which represented nearly half of the total lipid, yielded two glycosides for which the structures O-alpha-d-glucopyranosyl-(1-->1)-d-glycerol and O-alpha-d-glucopyranosyl-(1-->2)-O-alpha-d-glucopyranosyl-(1-->1)-d-glycerol were established. 3. The ratio of monoglucosyl diglyceride to diglucosyl diglyceride increased with the age of the culture, though the total glycolipid concentration remained virtually constant. The glycolipid concentration was unaffected by the addition of cholesterol to the culture medium. 4. The phospholipid fraction consisted of two components, phosphatidylglucose and phosphatidylglycerol. Organisms harvested at acidic pH also contained O-amino acyl esters of phosphatidylglycerol. No lipids containing inositol could be detected.

The phospholipids of Mycoplasma hominis type 2 strain 07 are composed almost entirely of phosphatidyl glycerol. Traces of other glycerophospholipids may exist. No glycolipids are found. The phospholipids of Mycoplasma sp. avian strain J are composed of diphosphatidyl glycerol, which predominates in older cultures, a monoacyl glycerophosphoryl glycerophosphate, which may serve as a precursor of diphosphatidyl glycerol, and phosphatidyl glycerophosphate. This organism also contains cholesteryl glucoside and an unidentified glycolipid which appears to be similar to a monoglucosyl diglyceride. No turnover or radioisotope labeling of the phospholipids occurs during metabolism. This lack of turnover during growth is indicative of a structural role for these glycerophospholipids. A concomitant decrease of monoacyl glycerophosphoryl glycerophosphate and increase of diphosphatidyl glycerol occurs during growth.

Bacillus stearothermophilus NCA 2184 lost viability and subsequently released cytoplasmic components when suspended in 0.1 M tris(hydroxymethyl)aminomethane (Tris) buffer (pH 7.2) and incubated at 60 degrees C. Cell lysis was prevented by the addition of 10 mM CaCl2 to the Tris-buffer suspension. Cells which were incubated under anaerobic conditions for 20 min in the growth medium before they were collected were stable in the Tris-buffer suspension without added calcium. Anaerobic incubation effected an increase in membrane cardiolipin which appeared to be related to the increase in the thermostability of the cells.

The phospholipids of Mllycoplasina laidlawii strain B consist of phosphatidyl glucose and an unidentified compound. This unidentified phospholipid (fraction H) was shown to be neither a nitrogen-containing compound, a plasmalogen,

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