Elucidating the Pseudomonas aeruginosa fatty acid degradation pathway: identification of additional fatty acyl-CoA synthetase homologues.

The fatty acid (FA) degradation pathway of Pseudomonas aeruginosa, an opportunistic pathogen, was recently shown to be involved in nutrient acquisition during BALB/c mouse lung infection model. The source of FA in the lung is believed to be phosphatidylcholine, the major component of lung surfactant. Previous research indicated that P. aeruginosa has more than two fatty acyl-CoA synthetase genes (fadD; PA3299 and PA3300), which are responsible for activation of FAs using ATP and coenzyme A. Through a bioinformatics approach, 11 candidate genes were identified by their homology to the Escherichia coli FadD in the present study. Four new homologues of fadD (PA1617, PA2893, PA3860, and PA3924) were functionally confirmed by their ability to complement the E. coli fadD mutant on FA-containing media. Growth phenotypes of 17 combinatorial fadD mutants on different FAs, as sole carbon sources, indicated that the four new fadD homologues are involved in FA degradation, bringing the total number of P. aeruginosa fadD genes to six. Of the four new homologues, fadD4 (PA1617) contributed the most to the degradation of different chain length FAs. Growth patterns of various fadD mutants on plant-based perfumery substances, citronellic and geranic acids, as sole carbon and energy sources indicated that fadD4 is also involved in the degradation of these plant-derived compounds. A decrease in fitness of the sextuple fadD mutant, relative to the ΔfadD1D2 mutant, was only observed during BALB/c mouse lung infection at 24 h.