The Effect of Exogenous Fatty Acids on Fatty Acid Metabolism in Escherichia coli K-12

Several different Escherichia coli K-12 strains have been investigated for evidence of control of fatty acid metabolism in response to exogenous fatty acid supplementation. [14C]-Acetate incorporation into lipid was used to identify the synthesized fatty acids recovered from the cell and the culture fluid. The identity and amounts (micrograms) of these fatty acids were determined by gas-liquid chromatography. When oleic acid is present in the growth medium as supplement, synthesized unsaturated fatty acids decrease in the cultures of two strains; furthermore, turnover of synthesized fatty acids via β oxidation can not occur in one of these strains. Taken together, these observations show that there is regulation of unsaturated fatty acid synthesis in these two strains. A third strain shows a less well defined response to oleate supplementation while an unsaturated fatty acid auxotroph from this strain clearly accumulated saturated and β-hydroxy fatty acids. The difference between strains with respect to regulation of synthesis may be explained partly in terms of differences in the β oxidation activities of the cells. The composition of the synthesized fatty acids recovered from the medium is consistent with the release of lipopolysaccharide and phospholipid from the outer membrane of the cell envelope.