It has been shown earlier that the unsaturated fatty acid biosynthetic capability of Mycoplasma sp. KHS is practically nil. This study has utilized this organism as a representative member of the sterol-nonrequiring mycoplasmas and has demonstrated its inherent ability to form long-chain monoenoic fatty acids when supplied with appropriate precursors. The use of palmitoleic (C16Δ9,10) and cis-5,6-tetradecenoic acids has revealed that the position of unsaturation within these precursors influences to a considerable degree the subsequent abilities of this mycoplasma to form a particular positional isomeric octadecenoic acid from them. Under the conditions studied, the formation as well as the absorption of cii-vaccenic acid (G18Δ11,12) by whole cells was favored over that of its isomer, oleic acid (C18Δ9,10). Analogies are drawn and the results discussed in terms of recent bacterial lipid findings. For example, the data obtained tend to implicate a possible common branching point in fatty acid biosynthesis by seemingly reflecting a sensitive point in saturated fatty acid biosynthesis amenable to varying degrees of disturbance depending upon the monoenoic acid supplied to the growth medium. It was found that although unsaturated fatty acid elongation does occur upon addition of suitable precursors, a concomitant but increasing disturbance on saturated acid biosynthesis also occurs as the chain length of the unsaturated acid precursor added is decreased. Major saturated fatty acid biosynthesis terminated at a chain length of 16 carbon atoms. No increase in either the saturated or unsaturated fatty acid content of this organism was noted when the precursor added was β-hydroxydecanoic acid. The results obtained with a similar but opposite geometrici somer, palmitelaidic acid, have provided insights into the specificity of fatty acid utilization by Mycoplasma sp. KHS. These findings have pointed to at least two “sets” of enzymes being involved in the utilization of long-chain monoenoic fatty acid by whole cells of this nonsterol-requiring mycoplasma: (a) those unconcerned with geometrical or positional isomerization but necessary for long-chain fatty acid incorporation into complex structural lipids and (b) those involved in the elongation of only those acids with the cis configuration. Similarities and differences in fattyacid interconversions between bacteria and this mycoplasma are discussed. © 1969, American Chemical Society. All rights reserved.
