Discovery of a novel dehalogenase from Achromobacter mucicolens for PFAS defluorination

Here, we report the purification and characterization of a haloacid dehalogenase type II (HAD-II) enzyme capable of direct and cell-free enzymatic defluorination by cleaving the resilient C-F bond in perfluorooctanoic acid (PFOA). While conventional remediation strategies rely on energy-intensive chemical/thermal methods, biological alternatives are limited by long whole-microbiome incubations and poorly understood metabolic pathways. We discovered a novel HAD-II enzyme from Achromobacter mucicolens found in PFAS-contaminated lacustrine sediment, providing evidence of real-time microbial adaptation. Within 24-hour incubation, the system released approximately 0.55 ppm fluoride (17% yield) from a 5ppm PFOA (equivalent to maximum fluoride of 3.24 ppm) in recombinant enzyme assays. Structural and phylogenetic analyses reveal that the newly discovered HAD-II belongs to a deeply divergent lineage sharing only 25% sequence identity with the previously characterized Delftia homologue while preserving the core HAD-like catalytic fold. Comparative molecular docking further elucidated this functional divergence, demonstrating that PFOA adopts a productive binding orientation near the conserved catalytic Asp15 within the A. mucicolens active-site pocket, whereas the Delftia counterpart forces non-productive binding outside the catalytic site. Together, our work unveils a previously unrecognized Achromobacter -associated dehalogenase that mediates PFAS defluorination despite severe sequence divergence, offering a critical new paradigm for targeted biological remediation.