Fatty acid synthesis promoted by PA1895-1897 operon delays quorum sensing activation in Pseudomonas aeruginosa

Abstract PA1895-1897 is a quorum sensing (QS) operon regulated by the anti-activator LuxR homologue QscR in Pseudomonas aeruginosa. We aimed to investigate its impact on bacterial metabolism, and whether it contributes to the delayed QS activation. We performed liquid chromatograph-mass spectrometer–based metabolomics using wildtype PAO1, PA1895-1897-knockout mutant, and mutant with pJN105.PA1895-1897 overexpression vector at the OD600nm of 1.8. The impact of metabolites on QS signal molecule (3OC12-HSL and C4-HSL) concentrations, pyocyanin production, and QS gene (lasR, lasI, rhlR, and rhlI) expression was examined. Metabolomics analysis found that fatty acid biosynthesis had the highest fold enrichment among all metabolic pathways. Medium- and long-chain fatty acids including palmitoleic acid, 2,2-Dimethyladipic acid, undecanoic acid, methylglutaric acid, myristoleic acid, myristic acid, pentadecanoic acid, and some short-chain fatty acids (butyric acid, acetic acid, and caproic acid) were down-regulated by PA1895-1897 knockout, and up-regulated by PA1895-1897 overexpression. Among these fatty acids, palmitoleic acid and acetic acid were the predominantly abundant fatty acids affected by PA1895-1897 operon. When different doses of exogenous palmitoleic acid or acetic acid were added to the cultures of PA1895-1897 knockout mutants, their levels of 3OC12-HSL, C4-HSL, and pyocyanin were decreased in a dose-dependent manner. High doses of palmitoleic acid and acetic acid suppressed the mRNA expression of lasR, rhlR, and rhlI. Inhibition of fatty acid biosynthesis increased the production of 3OC12-HSL, C4-HSL, and pyocyanin in PA1895-1897-overexpressed culture. Our data suggest that fatty acid synthesis is promoted by PA1895-1897 operon, and contributes the delayed expression of QS phenotypes, furthering the understanding about the regulation of bacterial QS activation.