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In a horse serum-based medium containing a full complement of fatty acids, cells of Spiroplasma citri were seen to preferentially incorporate palmitic acid. In the same medium, which had a steryl ester-to-sterol ratio of 3.64, a steryl ester-to-sterol ratio of 0.23 was seen in the cells, cholesterol being preferentially incorporated over cholesteryl ester. Like most other mycoplasmas, S. citri was shown to be unable to synthesize fatty acids or esterify cholesterol. The neutral lipids of S. citri grown in a medium containing horse serum consisted of free cholesterol, cholesteryl ester, free fatty acids, triglycerides and diglycerides. All polar lipids were phospholipids, with no glycolipids detected. These phospholipids, which are characteristic of many mycoplasmas, are phosphatidyl glycerol, diphosphatidyl glycerol, and their lyso derivatives. Sphingomyelin was also incorporated when cells were grown on horse serum. A sterol requirement for the growth ofS. citri was confirmed using a serum-free medium supplemented with bovine serum albumin, palmitic acid, and various concentrations of sterols dissolved in Tween 80. The addition of palmitic acid stimulated growth but was not essential for growth. S. citri was shown to grow best on cholesterol and ,Bsitosterol and was able to grow on stigmasterol and ergosterol to a lesser degree. No growth was obtained using mevalonate, deoxycholate, or taurodeoxycholate as an alternative to sterol. S. citri was also able to grow when palmitic acid was replaced with oleic acid, linoleic acid, or linolenic acid. Alterations in the lipid composition of the growth medium and hence in the lipid composition of S. citri induced changes in the characteristic helical morphology of the cells, concurrent with loss of cell viability. Culture, age, and pH were also factors in determining cell morphology and viability.

A procedure is described for the purification of the cores of flagella sheared from Vibrio cholerae. V. cholerae is a monotrichous organism whose flagellar core (FC) is enclosed within a sheath. The purification procedure consists of several cycles of differential centrifugation and cesium chloride density-gradient ultracentrifugation in the presence of a neutral detergent, Triton X-100. Purity of the FC preparations is assessed by electron microscopy, polyacrylamide gel electrophoresis, and chemical analysis. The purified FC preparations are devoid of flagellar sheaths and free from detectable cell wall and cytoplasmic contamination. Antibody prepared in rabbits against purified FC reacts with the flagellum of intact V. cholerae or purified FC as seen by ferritin-labeled antibody studies. Purified FC is composed of a single protein subunit with an estimated molecular weight of 45,000 g/mol and a density of about 1.3 g/cm3.on July 16, 2020 by guest

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