Degradation of Benzo[ a ]pyrene by Mycobacterium vanbaalenii PYR-1

Abstract

ABSTRACT Metabolism of the environmental pollutant benzo[ a ]pyrene in the bacterium Mycobacterium vanbaalenii PYR-1 was examined. This organism initially oxidized benzo[ a ]pyrene with dioxygenases and monooxygenases at C-4,5, C-9,10, and C-11,12. The metabolites were separated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by UV-visible, mass, nuclear magnetic resonance, and circular dichroism spectral analyses. The major intermediates of benzo[ a ]pyrene metabolism that had accumulated in the culture media after 96 h of incubation were cis -4,5-dihydro-4,5-dihydroxybenzo[ a ]pyrene (benzo[ a ]pyrene cis -4,5-dihydrodiol), cis -11,12-dihydro-11,12-dihydroxybenzo[ a ]pyrene (benzo[ a ]pyrene cis -11,12-dihydrodiol), trans -11,12-dihydro-11,12-dihydroxybenzo[ a ]pyrene (benzo[ a ]pyrene trans -11,12-dihydrodiol), 10-oxabenzo[ def ]chrysen-9-one, and hydroxymethoxy and dimethoxy derivatives of benzo[ a ]pyrene. The ortho -ring fission products 4-formylchrysene-5-carboxylic acid and 4,5-chrysene-dicarboxylic acid and a monocarboxylated chrysene product were formed when replacement culture experiments were conducted with benzo[ a ]pyrene cis -4,5-dihydrodiol. Chiral stationary-phase HPLC analysis of the dihydrodiols indicated that benzo[ a ]pyrene cis -4,5-dihydrodiol had 30% 4 S ,5 R and 70% 4 R ,5 S absolute stereochemistry. Benzo[ a ]pyrene cis -11,12-dihydrodiol adopted an 11 S ,12 R conformation with 100% optical purity. The enantiomeric composition of benzo[ a ]pyrene trans -11,12-dihydrodiol was an equal mixture of 11 S ,12 S and 11 R ,12 R molecules. The results of this study, in conjunction with those of previously reported studies, extend the pathways proposed for the bacterial metabolism of benzo[ a ]pyrene. Our study also provides evidence of the stereo- and regioselectivity of the oxygenases that catalyze the metabolism of benzo[ a ]pyrene in M. vanbaalenii PYR-1.