Biodegradation of TDCPP by Chlorella pyrenoidosa: Kinetic, metabolic, and molecular mechanistic insights.

Abstract

Despite their frequent detection in industrial effluents and aquatic environments, the metabolic fate and microalgal detoxification mechanisms of highly recalcitrant chlorinated organophosphorus flame retardants (OPFRs), specifically TDCPP, remain poorly understood. This study integrated metabolite profiling, transcriptomics, and computational enzymology to elucidate TDCPP biotransformation by Chlorella pyrenoidosa. The microalgae achieved 71.3% removal within 12 days (1 mg/L initial concentration) primarily by biodegradation. The metabolic trajectory involved hydrolysis, hydroxylation, and dechlorination, featuring a sequential TDCPP-BDCPP-MDCPP hydrolysis cascade as the core detoxification route. TDCPP-CHO and MDCPP-H were tentatively identified as novel metabolic byproducts in a photosynthetic organism. Transcriptomics revealed the up-regulation of candidate degradation genes, such as purple acid phosphatase (PAP), along with the activation of the PSII repair cycle, central carbon metabolism, and amino acid biosynthesis to fuel the detoxification process. Furthermore, enzyme inhibition assays validated the in vivo participation of PAP as a contributing hydrolase. At the atomic level, molecular dynamics trajectories revealed that TDCPP stably anchors to the bimetallic (Fe³⁺-Mn²⁺) center via an exogenous oxygen μ-bridge, establishing the precise pre-reaction geometry required for efficient cleavage. This study elucidates the microalgal OPFRs detoxification mechanisms, guiding bio-augmented remediation strategies for industrial wastewaters and extreme contamination events.