Reductive-Oxidative Biodegradation of Bisphenol A under the Nitrate-Reducing Conditions: The Interplay with Carbon Metabolism and Nitrate Assimilation

Bisphenol A (BPA), a representative endocrine-disrupting chemical, poses significant threats to human and ecological health. While microbial BPA degradation under aerobic conditions is well-documented, the initiation and performance of degradation by alternative electron acceptors remain poorly characterized. In this study, we identified a reductive-oxidative pathway in an isolated Klebsiella pneumoniae strain under nitrate-reducing conditions. BPA degradation reached 49.7% within 120 h with NO₃^––N (10 mg/L) and glucose (7.5 g/L). Untargeted metabolomics proposed a sequential reductive-oxidative pathway: BPA was first reduced to 2,2-diphenylpropane (DPP), then hydroxylated, and cleaved by hydroxylases and dioxygenases (e.g., BsdC, HcaB). Isothermal titration calorimetry and molecular dynamics confirmed the key roles of the enzyme in BPA biodegradability, and proteomics revealed that metabolic reprogramming drove BPA degradation under nitrate-reducing conditions. Specifically, BPA upregulated carbon-metabolism enzymes to generate reducing equivalents for the initial reduction. Subsequent electron transfer from oxidized DPP intermediates, coupled with an assimilatory nitrate reduction, enabled complete degradation. These findings provide novel mechanistic insights into BPA biodegradation under nitrate-reducing conditions and establish a theoretical basis for bioremediation strategies in contaminated anaerobic ecosystems.