Selection and properties of Escherichia coli mutants defective in the synthesis of cyclopropane fatty acids

Mutants of E. coli K 12 defective in the synthesis of cyclopropane fatty acids (CFA) have been selected and isolated by a L [methyl ³H] methionine suicide procedure. Two mutants were isolated. Stationary phase cultures of both mutants contain <0.7% of the CFA content found in the parental strain. The CFA deficiency is attributed to a deficiency of CFA synthetase activity. Extracts of both mutants contain less than 10% of the CFA synthetase activity found in extracts of the parental strain. Experiments in which parental and mutant extracts were mixed indicate that the lack of activity in the mutant strains is not due to an inhibitor of CFA synthetase present in the mutant extracts. The authors have not yet detected a physiological phenotype for these mutants. These strains grow normally at various temperatures in a variety of media. The authors have tested survival (colony forming ability) in response to prolonged incubation in stationary phase, exposure to drying, and exposure to detergents, heavy metals, low pH, high salt concentration, and a variety of other environmental conditions. The survival of both mutants is identical to that of the parental strain under all conditions tested. The compositions (excepting the CFA) deficiency and metabolic turnover rates of the phospholipids of both mutant strains are indistinguishable from those of the wild type strain. The transport of several amino acids also seems normal in these mutants.