[Investigations on the fatty acid composition of lipids from Salmonella minnesota S and R forms (author's transl)].

Non-covalently bound lipids were extracted from 2 Salmonella minnesota S forms and 5 R mutants (chemotype Ra-Re) isolated from these strains. The lipids were subsequently analysed with regard to fatty acid composition. The extracts were free of lipid A, as determined by absence of beta-hydroxymyristic acid. The fatty acid distribution in the lipids of the two S forms, cultivated at 37 degrees C to the beginning of the stationary phase of growth, agreed very closely, and the values corresponded to those reported in the literature for S. typhimurium. In contrast, there was a progressive reduction in the content of C17- and C19-cyclopropane fatty acids, going from Ra-Rc mutants. The total cyclopropane fatty acids decreased from approximately 30% (Ra) to approximately 7% (Rc). The lipids from the Rd1 and the Re mutants had a fatty acid composition identical to that of the Rc mutant. The decrease in cyclopropane fatty acid content was compensated for in all strains by an increase in the corresponding unsaturated fatty acids (16:1; 18:1). Variations in the incubation temperature (30, 37, 41 degrees C) affected the ratio of the single fatty acids as determined for the Ra, Rc and Re mutants. The content of unsaturated fatty acids increased with the reduction in temperature, while the proportion of cyclopropane fatty acids decreased (stationary growth phase). These changes were much more pronounced with the Ra mutant than with the Rc and the Re mutants. The differences among the mutants with regard to fatty acid distribution were apparent at all temperature levels. In addition, the fatty acid composition of the lipids varied with the phase of growth, as already reported for E. coli and other gram-negative organisms. The content of cyclopropane fatty acids increased from the exponential to the stationary phases, with simultaneous reduction in the proportion of corresponding unsaturated fatty acids. Again, the lipid composition of the Ra mutant varied to a greater extent than did that of the Rc and the Re mutants. Similar changes appeared in the phosphatidyl ethanolamine fractions of the three mutants. There were also changes in the neutral lipids that agreed in part with those of the total lipids. The cause of the reduced cyclopropane fatty acid synthesis in S. minnesota R mutants possessing an incomplete LPS-core structure (Rb2-Re) is at present unknown. The physiological significance of these findings as well remains for the moment speculative, as the functional role of cyclopropane fatty acids in biological membranes has not yet been elucidated. Possible relations to membrane permeability and to transfer of antibiotics are discussed.