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Biological dehalogenation degradation was an important detoxification method for the ecotoxicity and teratogenic toxicity of fluorocorticosteroids (FGCs). The functional strain Acinetobacter pittii C3 can effectively biodegrade and defluorinate to 1 mg/L Triamcinolone acetonide (TA), a representative FGCs, with 86 % and 79 % removal proportion in 168 h with the biodegradation and detoxification kinetic constant of 0.031/h and 0.016/h. The dehalogenation and degradation ability of strain C3 was related to its dehalogenation genomic characteristics, which manifested in the functional gene expression of dehalogenation, degradation, and toxicity tolerance. Three detoxification mechanisms were positively correlated with defluorination pathways through hydrolysis, oxidation, and reduction, which were regulated by the expression of the haloacid dehalogenase (HAD) gene (mupP, yrfG, and gph), oxygenase gene (dmpA and catA), and reductase gene (nrdAB and TgnAB). Hydrolysis defluorination was the most critical way for TA detoxification metabolism, which could rapidly generate low-toxicity metabolites and reduce toxic bioaccumulation due to hydrolytic dehalogenase-induced defluorination. The mechanism of hydrolytic defluorination was that the active pocket of hydrolytic dehalogenase was matched well with the spatial structure of TA under the adjustment of the hydrogen bond, and thus induced molecular recognition to promote the catalytic hydrolytic degradation of various amino acid residues. This work provided an effective bioremediation method and mechanism for improving defluorination and detoxification performance., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Defluorination is a key factor in reducing biologically accumulated carcinogenic and teratogenic toxicity of fluoroglucocorticoids (FGCs). To enhance defluorination efficiency, a highly efficient defluorination-degrading strain Acinetobacter. pittii C3 was isolated, and the promotion mechanism through humic acid (HA)-mediated biotransformation was investigated. Optimal biodegradation conditions for Acinetobacter sp. pittii C3 were pH of 7.0, temperature of 25 ℃, and HA content of 5.5 mg/L, according to response surface methodology analysis. The attenuation rate constant and maximum defluorination percentage of triamcinolone acetonide (TA) in HA-mediated biotransformation system (HA-C3) were 3.99 × 10 -2 and 96%, respectively, which were 2.22 and 1.24 times higher than those in the unitary C3 biodegradation system (U-C3), respectively. The major defluorination pathways included elimination, hydrolysis, and hydrogenation, with contributions of 24.5%, 32.4%, and 43.1%, respectively. The bio-reductive hydrodefluorination rate was enhanced by 1.89 times that of HA-mediated, while the other two defluorination pathways exhibited insignificant changes. HA, as the congeries of negatively charged microbes and hydrophobic TA, accelerates the electron transfer rate between Acinetobacter. pittii C3 and TA through the quinone groups. Furthermore, the mutual conversion between the functional groups of hydroxyl oxidation and ketone reduction of HA provided electron donors for TA reductive defluorination and hydrogenation and electron acceptors for TA oxidation. This study provides an effective strategy for FGC-enhanced detoxification using natural HA., (Copyright © 2022. Published by Elsevier B.V.)