Biodegradation and toxicity attenuation of bisphenol A by Sphingopyxis granuli XYQ201: mechanism elucidation and...

Bisphenol A (BPA) is a widespread endocrine-disrupting contaminant in wastewater, and microbial biodegradation is a promising approach for its removal. However, BPA-degrading bacteria with clarified degradation products, reduced estrogenic activity after degradation, and demonstrated performance in real wastewater remain limited. In this study, a BPA-degrading bacterium, Sphingopyxis granuli XYQ201, was isolated from municipal wastewater and shown to utilize BPA as the sole carbon source. Strain XYQ201 completely removed 50 mg/L BPA within 38 h under laboratory conditions. Four major degradation products were identified by comparison with authentic standards, including 4-[2-hydroxy-2-(4-hydroxyphenyl)propyl]phenol, 4-[1-hydroxy-2-(4-hydroxyphenyl) propan-2-yl]phenol, 2,3-bis(4-hydroxyphenyl)propane-1,2-diol, and a previously unreported metabolite, 2,2-bis(4-hydroxyphenyl)propane-1,3-diol. Toxicological evaluation using a recombinant yeast bioreporter assay showed that the major hydroxylated metabolites had markedly lower estrogenic activity than BPA, indicating attenuation of estrogenic activity during BPA transformation. Genome analysis, quantitative PCR, and heterologous expression demonstrated that a plasmid-borne bisdAB-encoded two-component cytochrome P450 system is sufficient to initiate BPA hydroxylation and generates the mono-hydroxylated products. Public genomic and metagenomic analyses showed that putative bisdA/bisdB-like genes are phylogenetically diverse and occur in multiple natural and engineered environments. In BPA-spiked wastewater, inoculation with XYQ201 substantially enhanced BPA removal under a high-load condition. These results indicate that strain XYQ201 mediates BPA transformation through a P450-initiated hydroxylation pathway with reduced estrogenic activity of the major metabolites, and may serve as a candidate strain for bioaugmentation of BPA-contaminated wastewater.