Mapping of the fabA locus for unsaturated fatty acid biosynthesis in Escherichia coli

fabA mutants of Escherichia coli require an appropriate unsaturated fatty acid for growth. The fabA locus has now been mapped at minute 21.5 of the linkage map of E. coli. The locus is cotransduced with pyrD and aroA but not with pyrC, purB, or pdxC. The clockwise order of markers in the region is pdxC, aroA, cmlB, pyrD, fabA, pyrC.

Selection and characterization of an E. coli mutant defective in membrane lipid biosynthesis

A procedure is described for the selection of temperature-sensitive phospholipid mutants based upon radiation suicide of the wild-type organisms by tritiated L-glycerol-3-phosphate incorporated in the phospholipids. One of these mutants possesses an acyltransferase activity much more thermolabile than that of its parent. This mutant ceases growth and phospholipid biosynthesis immediately upon shift to a nonpermissive temperature although DNA, RNA, and protein continue to be synthesized. The phenotype of this mutant appears due to a single mutation by reversion analysis and by enzymatic analysis of temperature-resistant revertants.

Evidence for two genes specifically involved in unsaturated fatty acid biosynthesis in Escherichia coli

Unsaturated fatty acid auxotrophs of Eschericha coli have been divided into two distinct cistrons by extract complementation and genetic complementation based on abortive transduction. Lesions in one cistron result in the loss of the beta-hydroxydecanoyl thioester dehydrase which produces the first biosynthetic intermediate in unsaturated fatty acid formation. Evidence is presented which indicates that lesions in the second cistron result in the lack of a second enzyme specifically involved in the biosynthesis of unsaturated fatty acids.

Phospholipid alterations during growth of Escherichia coli

As cultures of Escherichia coli progressed from the exponential growth phase to the stationary growth phase, the phospholipid composition of the cell was altered. Unsaturated fatty acids were converted to cyclopropane fatty acids, and phosphatidyl glycerol appears to have been converted to cardiolipin. With dual isotope label experiments, the kinetics of synthesis of cyclopropane fatty acid for each of the phospholipids was examined in vivo. The amount of cyclopropane fatty acid per phospholipid molecule began to increase in phosphatidyl ethanolamine at a cell density below the density at which this increase was observed in phosphatidyl glycerol or cardiolipin. The rate of this increase in phosphatidyl glycerol or in cardiolipin was faster than the rate of increase in phosphatidyl ethanolamine. After a few hours of stationary-phase growth, all the phospholipids were equally rich in cyclopropane fatty acids. It is suggested that the phospholipid alterations observed are a mechanism to protect against phospholipid degradation during stationary phase growth. Cyclopropane fatty acid synthetase activity was assayed in cultures at various stages of growth. Cultures from all growth stages examined had the same specific activity in crude extracts.