METABOLIC PATHWAYS OF QUINOLINE, INDOLE AND THEIR METHYLATED ANALOGS BY DESULFOBACTERIUM-INDOLICUM (DSM-3383)

The transformation of quinoline, isoquinoline and 3-, 4-, 6- and 8-met hylquinoline by Desulfobacterium indolicum was compared with that of t he N-containing analogues indole and 1-, 2-, 3- and 7-methylindole. Th e metabolites were identified using high-performance liquid chromatogr aphy with UV detection, thin-layer chromatography, combined gas chroma tography/mass spectrometry and proton NMR spectroscopy. All degraded c ompounds were initially hydroxylated at position 2 by D. indolicum. A new degradation product of quinoline was observed in the second transf ormation step, where 3,4-dihydro-2-quinolinone accumulated. This ring- reduced compound was further transformed into unidentified products. T he transformation pathway of indole was characterized by well-known st eps through oxindole, isatin, and anthranilic acid. No further transfo rmation of the hydroxylated methyl analogues: 3- and 7-methyloxindole and 3- and 4-methyl-2-quinolinone, was observed within 162 days of inc ubation. These degradation products accumulated in stoichiometric amou nts, while 6- and 8-methyl-2-quinolinone were further degraded to 6- a nd 8-methyl-3,4-dihydro-2-quinolinone in stoichiometric amounts. Isoqu inoline, 2-methylquinoline and 1- and 2-methylindole were not degraded by D. indolicum. These observations indicate that a methyl group at o r close to position 2 results in blockage of the microbial attack, and that transformation of hydroxyquinolines methylated at the heterocycl ic ring also was blocked or sterically inhibited. An incomplete transf ormation of some methylated compounds was observed, e.g. for 3- and 6- methylquinoline and 3- and 7-methylindole, with residual concentration s of 0.5-4 mg/l in relation to initial concentrations of 10-15 mg/l.