Chemical composition of Azotobacter vinelandii cysts.

Cysts of Azotobacter vinelandii ATCC 12837 were germinated by exposure to 3.0 mm ethylenediaminetetraacetic acid (EDTA)-tris(hydroxymethyl)aminomethane buffer at pH 7.8, and their outer coats (exines) were purified by differential and isopycnic centrifugation. Electron micrographs of exine showed it to consist of multilayers of a three-membered sheet structure whose thickness was 7.0 to 7.5 nm. The inner, less electron-dense layer (intine) was also prepared from cysts by EDTA treatment, centrifugation, concentration, and dialysis. The exine consisted of 32% carbohydrate, 28% protein, 30% lipid, and 3.2% ash, with the ash comprised of 1.62% calcium, 0.02% magnesium, and 0.34% phosphorus. The amino acid composition of exine was similar to that of gram-negative bacterial cell walls. The intine consisted of 44% carbohydrate, 9.1% protein, 37% lipid, and 4.1% ash, with the ash comprised of 2.45% calcium, 0.02% magnesium, and 0.38% phosphorus. The carbohydrates of both exine and intine contained glucose, mannose, xylose, and rhamnose. Glucosamine and galactosamine were found only in the exines. The fatty acids consisted of normal, iso, and anteiso saturated fatty acids with 10 to 18 carbon atoms and mono-unsaturated C(11), C(16), and C(18) fatty acids. The exines contained mostly bound lipid, but intines contained primarily free lipid.