Printed in Great Britain = 73 The Effect of Straight-chain Saturated, Monoenoic and Branched-chain Fatty Acids on Growth and Fatty Acid Composition of Mycoplasma Strain Y

The fatty acid growth requirements of a sterol-requiring Mycoplasma (strain Y), unable to synthesize or alter the chain length of either saturated or unsaturated fatty acids, were investigated. In some cases adaptation was required for growth when mycoplasmas were transferred to media of differing fatty acid composition. No straight-chain saturated acid supported growth when tested alone, but good growth was obtained with three branched-chain acids (isopalmitate, isostearate and anteisoheptadecanoate) tested singly and with some straight-chain saturated acids when tested in pairs (e.g. when equal proportions of C12 and C,, acids were supplied together). Of the unsaturated fatty acids tested, cis-I a-octadecenoate and two trans-octadecenoates (elaidate and trans-vaccenate) supported good growth alone. Little or no growth was obtained with any cis-monoenoic acid of the oleic acid series unless a straight-chain acid was also supplied and both the chain length of the monoenoic acid and the position of the double bond had a marked effect on the range of saturated acids with which it could be successfully paired. With myrist-oleate, long-chain saturated acids of chain length C,,, CZz gave the best growth; with oleate the range extended from C,, to C,, (optimal at C1,) and with erucate from Clo to C18 (optimal at C15). When the double bond was near the carboxyl group, as in cis-6-octadecenoate, strain Y grew only when paired with C14 to C1, saturated acids; as it became further removed from the carboxyl group as in cis-vaccenate, addition of a single saturated acid from an extended range (Clo to C24) could support growth. Only those fatty acids supplied in the growth medium were present in the lipids of the organism, and in cases where strain Y grew well when a single fatty acid was supplied, this was the sole fatty acid found. Marked differences in morphology were observed in mycoplasmas of differing fatty acid composition