The outer membrane transporter FadL was involved in the uptake of C18  n-alkane for enhancement of biodegradation in Pseudomonas aeruginosa TJM4

AIMS: The removal of n-alkanes by bacteria is a promising strategy for bioremediation. Especially, the transmembrane transport of n-alkanes is a critical intermediate process for transfer and adsorption. Herein, the structure and function of two FadL outer membrane transporters in Pseudomonas aeruginosa TJM4 were explored to elucidate the impact on efficient removal of C18 n-alkanes. METHODS AND RESULTS: Phylogenetic analysis revealed considerable distinction in FadL sequences among strains involved in alkane catabolism. RT-qPCR analysis revealed that the expression of the two outer membrane transporter-encoding genes in strain TJM4, fadL1 and fadL2, was significantly upregulated in response to C18 n-alkane induction. To further investigate whether FadL was involved in the uptake and transport of C18 n-alkane, the fadL1 and fadL2 genes were deleted to generate mutants. Growth and degradation assays demonstrated that loss of the fadL gene reduced the ability of strain TJM4 to utilize and degrade C18 n-alkane, and FadL1 played a key role in the removal of C18 n-alkane. Moreover, the cell surface hydrophobicity (CSH) of the mutants was significantly lower than that of the wild-type (WT) strain TJM4. However, the complementation of fadL gene restored alkane degradation capacity and CSH of those mutant strains. These findings supported the role of FadL in enhancement of n-alkane catabolism. Finally, molecular docking analysis revealed hydrophobic interactions between the two FadL transporters and C18 n-alkane, in which Val, Leu, Ile, and Ala played a role in both complexes. CONCLUSIONS: Those results indicated that FadL was a pivotal step for removal of C18 n-alkane in strain TJM4. The pronounced differences in sequence between the two FadL transporters and their interaction sites with C18 n-alkane suggested that they might be substrate-specific involved in the n-alkane transport pathway of strain TJM4.