Degradation pathway of quinolines in a biofilm system under denitrifying conditions

Abstract

This article reports for the first time the degradation pathways of quinoline, isoquinoline, and methylquinolines by a mixed culture in a biofilm under nitrate-reducing conditions. A simple reverse-phase high-performance liquid chromatography method using ultraviolet detection at 223 nm for determination of seven quinoline analogues and 15 metabolites was developed, and gas chromatography-mass spectrometry and thin-layer chromatography analyses were used for identification. The inhibition of nitrification by the parent compounds and their degradation products was assessed by a nitrification toxicity test called MINNTOX. Quinoline and 3-, 4-, 6-, and 8-methylquinoline were all transformed by hydroxylation into their 2-hydroxyquinoline analogues (2-quinolinones), and isoquinoline was transformed into 1-hydroxyisoquinoline. 2-Methylquinoline was not transformed by this microcosm, likely due to the blockage at position 2 by the methyl group. The hydroxylated metabolites of isoquinoline and quinolines methylated at the heterocyclic ring were not transformed further, whereas metabolites of quinoline and quinolines methylated at the homocyclic ring were hydrogenated at position 3 and 4, and the resulting 3,4-dihydro-2-quinolinone analogues accumulated. Of these metabolites, only 3,4-dihydro-2-quinolinone from the degradation of quinoline was further transformed into unidentified products. All quinolines and their metabolites had inhibiting effects on the nitrifying bacteria at the same level (ppm) in the applied bioassay, indicating that the inhibition of the compounds was not influenced by the initial transformation reactions.

Time-resolved analysis of a denitrifying bacterial community revealed a core microbiome responsible for the anaerobic degradation of quinoline

“…In this study, we obtained a detailed picture of quinoline degradation under denitrifying conditions in a batch experiment using an inoculum from a quinoline degrading, anaerobic bioreactor. Earlier studies showed that quinoline biodegradation proceeded in the presence of nitrate, but came to a halt when the nitrate was depleted 10 , while Burland et al . found that benzene oxidation was more tightly coupled to incomplete reduction of nitrate to nitrite rather than its complete reduction to N 2 17 .…”

“…The accumulated CO 2 showed that respiratory metabolism by denitrification was the main degradation process, and the recovery of quinoline C at this stage suggested nearly complete mineralization. Until now, in the transformation study of quinoline and its derivatives under denitrifying, only two intermediate metabolites were identified (1H-2-oxoquinoline and 3,4-dihydro-1H-2-oxoquinoline) 10 , 11 . In this study, we also failed to detect any intermediate aromatic metabolites.…”

“…Studies conducted during the past decades have shown that quinoline is biodegradable under anoxic conditions, albeit slower than in the presence of oxygen 1 . Quinoline biodegradation under anoxic conditions has been demonstrated when nitrate 10 , 11 or sulfate are available as electron acceptors 12 , and has also been shown to take place under methanogenic conditions 13 . Present-day knowledge on the biochemical pathway of anaerobic quinoline degradation is limited and based on a few studies 1 , 4 , 11 .…”

Thauera and Azoarcus as functionally important genera in a denitrifying quinoline-removal bioreactor as revealed by microbial community structure comparison

“…In recent years, NPAH pollution has become a public health concern (Stuermer et al , 1982; O'Loughlin et al , 1996). Removal of quinoline under denitrifying conditions has been demonstrated (Li, 2001) and the degradation pathway has been proposed (Johanson, 1997), but little is known about the microbial diversity underlying this process. Key members of the functional microbial population that are responsible for the removal process have not been identified in many ecosystems.…”

Cross-feeding betweenThauera aminoaromaticaandRhodococcus pyridinivoransdrove quinoline biodegradation in a denitrifying bioreactor

“…Unexpectedly, none of them could metabolize quinoline, when it was used as sole carbon source, both under anaerobic and aerobic conditions. However, all four isolates could utilize 2-hydroxyquinoline, the derivative of quinoline, which was reported as the first degrading intermediate of quinoline (31). Data showed that about 80% of 50 mg/L 2-hydroxyquinoline was eliminated in MMHQ medium within 10 days under nitrate-reducing condition and no any accumulation of intermediates in the measured samples (Fig.…”