Proposed biosynthetic pathway of PQS, HHQ, HQNO and DHQ in Pseudomonas aeruginosa. AQs are derived from a condensation reaction between anthranilate and β-keto fatty acids. Anthranilate is derived from either the PhnAB/TrpEG or the KynABU metabolic pathways using either chorismate or tryptophan as precursors, respectively. Anthranilate is first activated with coenzyme A (CoA) by PqsA. Anthranilate-CoA and an activated β-ketodecanoate are condensed, possibly via the PqsBCD enzymes to HHQ, releasing CO2 and H2O. The monooxygenase PqsH converts HHQ to PQS. HQNO is derived from the same starting products as HHQ, but utilizes the additional monooxygenase PqsL. HHQ is not a precursor for HQNO. DHQ, which technically is not an AQ, is produced by PqsD independent of PqsB and PqsC.
