Biosynthetic pathway of Pseudomonas aeruginosa 4-hydroxy-2-alkylquinolines.

The role of intercellular communication in the regulation of bacterial multicellular behavior has received widespread attention, and a variety of signal molecules involved in bacterial communication have been discovered. In addition to the N-acyl-homoserine lactones, 4-hydroxy-2-alkylquinolines (HAQs), including the Pseudomonas quinolone signal, have been shown to function as signal molecules in Pseudomonas aeruginosa. In this study we unraveled the biosynthetic pathway of HAQs using feeding experiments with isotope-labeled precursors and analysis of extracted HAQs by gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. Our results show that the biosynthesis of various HAQ metabolites is directed via a common metabolic pathway involving a "head-to-head" condensation of anthranilic acid and beta-keto fatty acids. Moreover, we provide evidence that the beta-keto-(do)decanoic acids, crucial for the biosynthesis of the heptyl and nonyl derivatives of the 4-hydroxyquinolines in P. aeruginosa, are at least in part derived from a common pool of beta-hydroxy(do)decanoic acids involved in rhamnolipid biosynthesis.