Biodegradation pathways and mechanisms of perfluorooctanoic acid and perfluorooctanesulfonic acid via key enzymes in the marine microalga Chaetoceros calcitrans MZB-1

Abstract

Microalgae-mediated biodegradation of per- and poly-fluoroalkyl substances (PFASs) has gained significant attention. However, the degradation mechanism remains unclear, which is critical for optimizing biodegradation efficiency. This study aimed to elucidate the molecular mechanisms underlying perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) biodegradation by Chaetoceros calcitrans MZB-1 and reveal relevant degradation pathways. After cultivation for 15 days, the removal of PFOA and PFOS at initial concentration of 100 μg/L by alga MZB-1 was at 24.41 % and 29.16 %, respectively. Proteomics analysis identified significant upregulation of enzymes involved in PFOA/PFOS degradation, including cytochrome P450 monooxygenases (CYP450), haloacid dehalogenase, alkane monooxygenase, and taurine dioxygenase (TauD). Elucidation of the biodegradation mechanism revealed that PFOA underwent initial decarboxylation by CYP450 to form 1H-perfluoroheptane, followed by elimination, hydration, and isomerization reactions to generate 1 H,1H-perfluoroheptanol. This intermediate was further oxidized to the corresponding aldehydes and acids, ultimately producing perfluorohexanoic acid (PFHxA). For PFOS degradation, the process initiated with CF₂ unit removal to form perfluoroheptanesulfonic acid (PFHpS), followed by TauD-mediated C-S bond cleavage and sulfonate group elimination at the end of carbon chain, converting PFHpS to 1H-perfluoroheptane. Then, the carbon chain gradually shortened, producing perfluoroheptanoic acid (PFHpA). Molecular docking showed that interactions between CYP450 and PFOA, as well as TauD and PFOS, primarily involved hydrogen bonding and hydrophobic interactions.