Benz[ a ]anthracene Biotransformation and Production of Ring Fission Products by Sphingobium sp. Strain KK22

A soil bacterium, designated strain KK22, was isolated from a phenanthrene enrichment culture of a bacterial consortium that grew on diesel fuel, and it was found to biotransform the persistent environmental pollutant and high-molecular-weight polycyclic aromatic hydrocarbon (PAH) benz[a ]anthracene. Nearly complete sequencing of the 16S rRNA gene of strain KK22 and phylogenetic analysis revealed that this organism is a new member of the genusSphingobium . An 8-day time course study that consisted of whole-culture extractions followed by high-performance liquid chromatography (HPLC) analyses with fluorescence detection showed that 80 to 90% biodegradation of 2.5 mg liter−1 benz[a ]anthracene had occurred. Biodegradation assays where benz[a ]anthracene was supplied in crystalline form (100 mg liter−1 ) confirmed biodegradation and showed that strain KK22 cells precultured on glucose were equally capable of benz[a ]anthracene biotransformation when precultured on glucose plus phenanthrene. Analyses of organic extracts from benz[a ]anthracene biodegradation by liquid chromatography negative electrospray ionization tandem mass spectrometry [LC/ESI(−)-MS/MS] revealed 10 products, including twoo -hydroxypolyaromatic acids and two hydroxy-naphthoic acids. 1-Hydroxy-2- and 2-hydroxy-3-naphthoic acids were unambiguously identified, and this indicated that oxidation of the benz[a ]anthracene molecule occurred via both the linear kata and angular kata ends of the molecule. Other two- and single-aromatic-ring metabolites were also documented, including 3-(2-carboxyvinyl)naphthalene-2-carboxylic acid and salicylic acid, and the proposed pathways for benz[a ]anthracene biotransformation by a bacterium were extended.