Elucidating the functions of fabF1 and fabF2 in Pseudomonas aeruginosa: implications for fatty acid metabolism and pathogenicity

Abstract Background Pseudomonas aeruginosa is an opportunistic pathogen responsible for severe infections in immunocompromised individuals, including burn patients and those with cystic fibrosis. β-Ketoacyl-ACP synthases play essential roles in bacterial fatty acid metabolism, influencing both cellular function and pathogenicity. Two types of long-chain β-ketoacyl-ACP synthases have been identified: FabB and FabF. This study aims to elucidate the roles of the fabF1 and fabF2 genes in fatty acid biosynthesis and virulence of P. aeruginosa PAO1. Results Complementation assays in Escherichia coli revealed that fabF2 could functionally replace E. coli FabB, whereas FabF1 exhibited FabF-like activity. In P. aeruginosa PAO1, deletion of fabF1 significantly reduced cis-vaccenic acid levels while increasing palmitoleic acid, whereas deletion of fabF2 had no measurable effect. The double mutant exhibited a pronounced reduction in cis-vaccenic acid levels. Virulence assays demonstrated that the ΔfabF1 strain exhibited a 63% decrease in rhamnolipid production, while the ΔfabF2 strain showed a 45% reduction. The double mutant retained only 28% of wild-type rhamnolipid levels. Furthermore, pyoverdine secretion was markedly reduced in the double mutant, and pyocyanin production was impaired. Motility assays indicated diminished swimming, twitching, and swarming abilities in the mutants. Additionally, proper expression levels of fabF2 were required to genetically complement fabF2 deletion in the mutant strain, as both overexpression and insufficient expression failed to restore the mutant phenotype effectively. Conclusions These findings highlight the critical roles of fabF1 and fabF2 in fatty acid biosynthesis, virulence factor production, and motility in P. aeruginosa. This study provides new insights into the functional divergence of FabF homologs and identifies potential targets for antimicrobial development.