Metabolism of fluoranthene by mycobacterial strains isolated by their ability to grow in fluoranthene or pyrene

Abstract

Mycobacterium sp. strains CP1, CP2, CFt2 and CFt6 were isolated from creosote-contaminated soil due to their ability to grow in pyrene (CP1 and CP2) or fluoranthene (CFt2 and CFt6). All these strains utilized fluoranthene as a sole source of carbon and energy. Strain CP1 exhibited the best growth, with a cellular assimilation of fluoranthene carbon of approximately 45%. Identification of the metabolites accumulated during growth in fluoranthene, the kinetics of metabolites, and metabolite feeding studies, indicated that all these isolates oxidized fluoranthene by the following two routes: the first involves dioxygenation at C-1 and C-2, meta cleavage, and a 2-carbon fragment excision to produce 9-fluorenone-1-carboxylic acid. An angular dioxygenation of the latter yields cis-1,9a-dihydroxy-1-hydrofluorene-9-one-8-carboxylic acid, which is further degraded via 8-hydroxy-3,4-benzocoumarin-1-carboxylic acid, benzene-1,2,3-tricarboxylic acid, and phthalate; the second route involves dioxygenation at C-2 and C-3 and ortho cleavage to give Z-9-carboxymethylenefluorene-1-carboxylic acid. In addition, the pyrene-degrading strains CP1 and CP2 possess a third route initiated by dioxygenation at positions C-7 and C-8, which--following meta cleavage, an aldolase reaction, and a C(1)-fragment excision--yields acenaphthenone. Monooxygenation of this ketone to the corresponding quinone, and its subsequent hydrolysis, produces naphthalene-1,8-dicarboxylic acid. The results obtained in this study not only complete and confirm the three fluoranthene degradation routes previously proposed for the pyrene-degrading strain Mycobacterium sp. AP1, but also suggest that such routes represent general microbial processes for environmental fluoranthene removal.