Benzo[a]pyrene degradation by Kefir-derived microbiota: medium optimization and metabolic pathways

Benzo[a]pyrene (BaP) is a highly carcinogenic and environmentally persistent polycyclic aromatic hydrocarbon (PAH) due to its low bioavailability and resistance to degradation. Microbial fermentation is a promising strategy to eliminate PAH residues in food processing, but the underlying mechanisms remain poorly characterized. Here, we optimized BaP biodegradation by Kefir-derived microorganisms using the Plackett-Burman design and response surface methodology (RSM). Under optimal conditions (12.50 mL of the trace element solution, 1.78 g/L Na₂HPO₄·2H₂O, and 2.88 g/L NaCl), the microorganisms achieved a degradation efficiency of 51.78%. Meta-transcriptomic analysis postulated two key degradation pathways: (I) 3,4-dioxygenase (α and β subunits) catalyzes the initial dioxygenation to produce phenanthrene, and (II) a fluorene-mediated transformation facilitates extensive degradation via the salicylic and phthalic acid pathways. These findings indicate the potential of Kefir-derived microbiota to detoxify BaP in food systems.