Metabolism of Benzo[a]pyrene by Paenibacillus sp. PRNK-6 through novel metabolite phenalene-1,9-dicarboxylic acid

Abstract

Benzo[a]pyrene (BaP) is a persistent carcinogenic environmental pollutant with high bioaccumulation potential and is resistant to bacterial biodegradation. Therefore, its removal from the biosphere is a priority. In the current study, the bacterial culture Paenibacillus sp. PRNK-6 was evaluated for the degradation of BaP. Paenibacillus sp. PRNK-6 efficiently utilizes BaP as a sole carbon source and degrades 89.43% of BaP within 120 h at an initial concentration of 100 mg L⁻¹. Maximum growth was observed at 96 h with 28.96 × 10⁷ colony-forming units (CFU). The BaP metabolic intermediates were characterized by High-performance liquid chromatography (HPLC) and, Gas chromatography-mass spectrometry (GC-MS). Based on the metabolite characterization, utilization of probable metabolic intermediates, and investigation of the enzyme involved, a putative pathway of the BaP degradation in PRNK-6 was proposed. The metabolites formed includes a novel ring cleavage metabolite phenalene-1,9-dicarboxylic acid. The two terminal monoaromatic metabolites catechol and protocatechuate (PCA) undergo ring fission by catechol 1,2-dioxygenase and protocatechuate 3,4-dioxygenase, individually and get into the tricarboxylic acid (TCA) cycle. In both pathways there is no accumulation of any dead-end products. The results suggest that the strain PRNK-6 could be a promising biodegradation tool for high molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) like BaP and may be equally used for bioremediation of other polycyclic aromatic hydrocarbons (PAHs).