Enrichment culture experiments employing soil and water samples obtained from petroleum-contaminated environments succeeded in the isolation of a pure culture possessing the ability to utilize quinoline as a sole nitrogen source but did not utilize quinoline as a carbon source. This culture was identified as Pseudomonas ayucida based on a partial 16S rRNA gene sequence, and the strain was given the designation IGTN9m. Examination of metabolites using thin-layer chromatography and gas chromatography-mass spectrometry suggests that P. ayucida IGTN9m converts quinoline to 2-quinolinone and subsequently to 8-hydroxycoumarin. Resting cells of P. ayucida IGTN9m were shown to be capable of selectively removing about 68% of quinoline from shale oil in a 16-h treatment time. These results suggest that P. ayucida IGTN9m may be useful in petroleum biorefining for the selective removal of organically bound nitrogen from petroleum.