Biodegradation characteristics of quinoline by Pseudomonas putida

A quinoline-degrading strain was isolated from activated sludge of the municipal wastewater treatment plant and identified as Pseudomonas putida on the basis of its partial 16S rRNA gene sequence analysis. The characteristics of quinoline degradation were investigated. The experimental results showed that quinoline at the concentration of 500 mg/L could be completely removed within 3 h, but could not be mineralized because special pigments were observed in the process of quinoline biodegradation. The N-atom in the quinoline ring was released as NH3; some metabolic intermediates were identified, including 2-hydroxyquinoline, 2,8-dihydroxyquinoline and 8-hydroxycoumarin. The metabolic pathway of quinoline by P. putida was tentatively proposed, that is, via 8-hydroxycoumarin pathway, namely, the biodegradation was initiated by hydroxylation at position 2 to form 2-oxo-1,2-dihydroquinoline (2-hydroxyquinoline), which was then oxidized to 8-hydroxy-2-oxo-1,2-dihydro-quinoline (2,8-dihydroxyquinoline) and 8-hydroxycoumarin.