Bacterial Mutants for the Study of Lipid Metabolism

This chapter discusses the bacterial mutants for the study of lipid metabolism. The major advantage to using the bacterium Escherichia coli for biochemical investigations is the possibility of genetic manipulation. Genetic methods may be used to eliminate specific enzymes from the cell, allowing unambiguous allocation of their in vivo role. The fatty acid composition of E. coli may be altered by feeding a variety of fatty acids to mutants defective in fatty acid biosynthesis. The fabD and fabE mutants are defective in the synthesis of all fatty acids, and were isolated as temperature-sensitive mutants. Supplementation of fabD or fabE mutants with saturated fatty acids plus unsaturated fatty acids (UFA) is only partly successful in maintaining growth at the restrictive temperature. The fabA and fabB mutants are specifically defective in the synthesis of UFA and may be supplemented with a variety of fatty acids, including cis- and trans-UFA, cyclopropane, branched, and halogenated fatty acids. A third mutation with no phenotype is cfa. These mutants have a defective cyclopropane fatty acid synthase and are deficient in the conversion of unsaturated fatty acids to their cyclopropane derivatives. This conversion occurs after the fatty acyl residues are attached to the phospholipids and happens only as cells enter the stationary phase.