Abstract
Abstract 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.
Highlights
When oleic acid is present in the growth medium as supplement, synthesized unsaturated fatty acids decrease in the cultures of two strains; turnover of synthesized fatty acids via /I oxidation can not occur in one of these strains
There is a suppression of unsaturated fatty acid derived from synthesis in strain AB1623 (Culture 2 versus 1) and in strain K1060R (Culture 4 versus 3)
For K1060R the distribution of endogenous product in the supplemented culture x amount of unsaturated fatty acid (Culture 4) approaches that observed for the fatty acid auxotroph
Summary
Several different Escherichia coZi K-12 strains have been investigated for evidence of control of fatty acid metabolism in response to exogenous fatty acid supplementation. Radioactive Label&y lo Identify b'clt@J Acids Derived from Synthesis--Cells grown on the same medium to be used for lubcling were harvested at 30,000 x y f’or JO min at room temper:Lture and washed once with minimal medium They were thr,Il resuspended at a cout*etltmtion of about IO8 cells per ml iu ,50 ml of fresh growth medium containing glycerol (or succinattl), essential nutrients for the particular strain, acetate, yeast extract, and oleate with or without Brij 35 (as indicated in tht text). Thin Layer Chromatography-Ether extractable radioactivity Gas-Liquid Chromatography for Separation and Measurement obtained from hydrolyzed material was analyzed directly by of Absolute Amounts of Fatty Acid-Fatty acidmethyl esterswere chromatographyon Silica Gel H Stahl (Merck, Darmstadt) of analyzedfor amount (micrograms)on a Varian Aerographmodel.
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