Fatty Acid Replacements in a Fatty Acid Auxotroph of Escherichia coli

Unsaturated fatty acids having structural features which are different from those of the monoenoic acids normally synthesized by Escherichia coli can serve as growth factors for an auxotroph requiring unsaturated fatty acids. These analogues were incorporated into the phospholipids, as shown by gas-liquid and thin-layer chromatographic analysis of the phospholipid fatty acid composition. Some of these fatty acids were cisDelta(5)- and cis-Delta(9)-tetradecenoic, cis-Delta(11)-eicosenoic, cis,cis-Delta(11,14)-eicosadienoic, cis,cis,cis-Delta(11,14,17)-eicosatrienoic, trans-Delta(9)- and trans-Delta(11)-octadecenoic acids. Although partial degradation of some of these analogues to shorter even-chain homologues occurred, chain elongation of the exogenous fatty acids was not detected. Trans-olefinic acids were utilized without stereochemical or positional isomerization. These studies provide a basis for exploring the properties of the fatty acids and phospholipids required for the formation, structure, and function of membranes.