Quantitative effects of unsaturated fatty acids in microbial mutants. VI. Selective growth responses of yeast and bacteria to cis-octadecenoate isomers.

The full series of positional isomers of cis-octadecenoate were tested for their suitability in meeting the nutritional requirement for unsaturated fatty acids by mutants of Escherichia coli and Saccharomyces cerevisiae that were unable to synthesize unsaturated fatty acids. Quantitative comparisons of the efficiencies of the various isomers showed a range from 0-48 cells per femtomole for the prokaryotic cells and 0-5 for eukaryotic cells. The delta 5 isomer was much more effective than the delta 6 isomer with the bacterial cells whereas the reverse was true with the yeast cells. In general, isomers containing a cis ethylenic bond between carbons 7 and 12 were able to support extensive growth of either type of mutant. Since all of the various isomers were incorporated into cellular lipids by both types of microorganism, the different efficiencies observed in supporting growth were not a simple reflection of the inability of an acid to be esterified. The differences may reflect the suitability of the resultant esterified product to function as a normal membrane lipid. The contents of various fatty acids in the cellular phospholipids when growth ceases may have a linearly cumulative relationship to the degree of expansion of the acyl chains.