Intracellular transformation rates of fatty acids are influenced by expression of the fatty acid transporter FadL in Escherichia coli cell membrane

Fatty acids have a low permeability through the cell membrane. Therefore, the intracellular biotransformation of fatty acids can be slow due to supply limitations. The effects of expression level of the fatty acid transporter FadL in Escherichia coli on the biotransformations were investigated. The enhanced expression of FadL led to 5.5-fold increase of the maximum reaction rate V_max (i.e., 200 μmol/min per g dry cells (200 U/g dry cells)) of the recombinant E. coli expressing a hydratase of Stenotrophomonas maltophilia in the periplasm with respect to hydration of oleic acid. The FadL expression level was also critical for oxidation of 12- and 10- hydroxyoctadecanoic acid by the recombinant E. coli expressing an alcohol dehydrogenase (ADH) of Micrococcus luteus. In addition, the multistep biotransformation of ricinoleic acid into the ester (i.e., (Z)-11-(heptanoyloxy)undec-9-enoic acid) by the recombinant E. coli expressing the ADH of M. luteus and a Baeyer-Villiger monooxygenase of Pseudomonas putida KT2440 was 2-fold increased to 40 U/g dry cells with expression of FadL to an appropriate level. The FadL expression level is one of the critical factors to determine whole-cell biotransformation rates of not only long chain fatty acids but also hydroxy fatty acids. This study may contribute to whole-cell biocatalyst engineering for biotransformation of hydrophobic substances.