SUMMARY: var. requires for growth a number of preformed lipid precursors. Media containing glycerol, cholesterol, a saturated and an unsaturated fatty acid, defatted bovine serum albumin and an additional defatted serum protein fraction (Fraction C) can supply these requirements. Albumin is believed to function by binding fatty acids, and Fraction C by binding cholesterol. The requirement for a saturated fatty acid can be satisfied by myristic, palmitic, stearic or margaric acid, lauric acid being less effective. The requirement for an unsaturated fatty acid can be satisfied by oleic acid, linoleic and linolenic acids being less effective. Organisms incubated in a medium deficient in either glycerol, the Fraction C + cholesterol system, or oleate, but adequate with respect to all other nutrients, died rapidly. Death was accompanied by lysis. Death due to a deficiency of glycerol or of cholesterol was prevented either by the omission of uracil (an essential nutrient) or by addition of chloramphenicol. Death due to oleate deficiency was not prevented by the omission of uracil. Morphological changes which resulted from each of these deficiencies are illustrated by electron micrographs. The hypothesis is advanced that glycerol, cholesterol and long-chain fatty acids are all needed for the synthesis of an undetermined cell component which is necessary for the structural integrity of the cell, and that the synthesis of this is more sensitive to a deficiency of these nutrients than is the synthesis of cytoplasm.


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