Transport of long-chain fatty acids by Escherichia coli: mapping and characterization of mutants in the fadL gene.

A new locus (fadL) that is required for the utilization of long-chain fatty acids has been mapped and partially characterized in an Escherichia coli mutant. The fadL locus has been mapped at 50 min on the chromosome. A mutant bearing a defect in this locus cannot utilize long-chain fatty acids as a sole carbon source. Derivatives of this mutant that can grow on decanoate (termed fadR) are capable of growth on medium-chain but not long-chain fatty acids. It is believed that the fadL mutants is defective in the transport of long-chain fatty acids into the cell for the following reasons: (i) fadR fadL strains can oxidize in vivo decanoate but not oleate; (ii) neither fadL nor fadR fadL strains can incorporate oleate into their membrane lipids; (iii) the activity of the acyl-CoA synthetase (EC 6.2.1.3) in fadR fadL strains is comparable to the acyl-CoA synthetase activity in fadR fadL+ strains; and (iv) in vitro extracts from fadR fadL+ strains. If the above hypothesis is correct, the uptake of long-chain fatty acids by E. coli requires at least two gene products.