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Polar biotransformation products have been identified as causative agents for the eventual increase in genotoxicity observed after the bioremediation of PAH-contaminated soils. Their further biodegradation has been described under certain biostimulation conditions; however, the underlying microorganisms and mechanisms remain to be elucidated. 9,10-Anthraquinone (ANTQ), a transformation product from anthracene (ANT), is the most commonly detected oxygenated PAH (oxy-PAH) in contaminated soils. Sand-in-liquid microcosms inoculated with creosote-contaminated soil revealed the existence of a specialized ANTQ degrading community, and Sphingobium sp. AntQ-1 was isolated for its ability to grow on this oxy-PAH. Combining the metabolomic, genomic, and transcriptomic analyses of strain AntQ-1, we comprehensively reconstructed the ANTQ biodegradation pathway. Novel mechanisms for polyaromatic compound degradation were revealed, involving the cleavage of the central ring catalyzed by Baeyer–Villiger monooxygenases (BVMO). Abundance of strain AntQ-1 16S rRNA and its BVMO genes in the sand-in-liquid microcosms correlated with maximum ANTQ biodegradation rates, supporting the environmental relevance of this mechanism. Our results demonstrate the existence of highly specialized microbial communities in contaminated soils responsible for processing oxy-PAHs accumulated by primary degraders. Also, they underscore the key role that BVMO may play as a detoxification mechanism to mitigate the risk posed by oxy-PAH formation during bioremediation of PAH-contaminated soils.

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