Involved in cellular response to chemical stress and may contribute to resistance toward antimicrobial natural compounds as well as drugs. Catalyzes the methylation and detoxification of the P.aeruginosa toxin 2-heptyl-1-hydroxy-4(1H)-quinolinone (HQNO) to 2-heptyl-1-methoxy-4(1H)-quinolinone (HMOQ). 2-heptyl-1-hydroxy-4(1H)-quinolinone + S-adenosyl-L-methionine = 2-heptyl-1-methoxy-4(1H)-quinolinone + H(+) + S-adenosyl-L-homocysteine Monomer. By salicylate and at higher concentrations by para-aminosalicylate (PAS) (at protein level). Belongs to the methyltransferase superfamily.