Enzymatic cleavage of C–F bonds in per- and polyfluoroalkyl substances (PFAS) is largely unknown but avidly sought to promote systems biology for PFAS bioremediation. Here, we report the reductive defluorination of α, β-unsaturated per- and polyfluorocarboxylic acids by Acetobacterium spp. Two critical molecular features in Acetobacterium species enabling reductive defluorination are (i) a functional fluoride efflux transporter (CrcB) and (ii) an electron-bifurcating caffeate reduction pathway (CarABCDE). The fluoride transporter was required for detoxification of released fluoride. Car enzymes were implicated in defluorination by the following evidence: (i) only Acetobacterium spp. with car genes catalyzed defluorination; (ii) caffeate and PFAS competed in vivo ; (iii) models from the X-ray structure of the electron-bifurcating reductase (CarC) positioned the PFAS substrate optimally for reductive defluorination; (iv) products identified by ¹⁹ F-NMR and high-resolution mass spectrometry were consistent with the model. Defluorination biomarkers identified here were found in wastewater treatment plant metagenomes on six continents.

Polyfluoroalkylether substances (ether PFAS) are widely detected in the environment with limited knowledge of their environmental fate via biological processes. This study reports the microbial transformation of environmentally relevant ether PFAS and similar structures and important microbial groups involved in the anaerobic biotransformation process. The investigated ether PFAS include mono- and dichlorinated ones such as 6:2 chlorinated polyfluorooctane ether sulfonate (F53-B) and 6,7-dichloroperfluoro-5-oxaheptanoic acid, as well as unsaturated ones such as sodium p-perfluorous nonenoxybenzenesulfonate (OBS) and the Nafion Byproduct 1 (NBP1). The presence of chlorine-substitution and unsaturated carbon facilitated the biotransformation and defluorination of ether PFAS under anaerobic or aerobic conditions. For fully halogenated ether PFAS, biotransformation only occurred in anaerobic conditions via dechlorination (reductive, eliminative, and hydrolytic), hydrolytic O-dealkylation, and reductive defluorination, forming less fluorinated and shorter chain products. Strong evidence was obtained from community and pure culture experiments for the involvement of cobalt-enzyme-dependent microorganisms, such as Sporomusa sphaeroides, in the initial dechlorination step during the biotransformation of chlorinated ether PFAS. Meanwhile, microorganisms independent of cobalt-enzymes, such as Desulfovibrio aminophilus, were responsible for the biotransformation of non-chlorinated unsaturated ether PFAS (e.g., NBP1), especially for the hydrolytic O-dealkylation reaction. The findings provide significant insights of the fate of ether PFAS in anaerobic environments and underscore the cooperation of different microbial groups in a community to achieve further transformation and higher defluorination.

Chlorinated per- and polyfluoroalkyl substances (Cl-PFAS) represent an important subgroup in replacement chemicals for legacy PFAS, and they have been detected in various environments including water bodies, soil, as well as air particles. However, the biodegradability of these chemicals is largely unknown. A recent study reported dechlorination triggered anaerobic biodefluorination of Cl-PFCAs by activated sludge communities. In this study, we further investigated the biodefluorination of Cl-PFCAs by pure cultures. Six of ten selected Cl-PFCAs displayed significant defluorination by Acetobacterium bakii , and corresponding pathways were proposed according to transformation product analysis. Several additional Acetobacterium species were all capable of defluorinating 3,5,7,8-tetrachloro-2,2,3,4,4,5,6,6,7,8,8- undecafluorooctanoic acid (CTFE4) with >50% removal of organic fluorine. On the contrary, Clostridium homopropionicum cannot defluorinate CTFE4. Crude protein extraction experiment showed that the enzymes responsible for CTFE4 dechlorination and defluorination required anaerobic atmosphere to function. Differential gene expression was analyzed according to RNA sequencing analysis, and the results indicated vitamin B12 related enzymes may involve in CTFE4 dechlorination.

Owing to their small size and surface hydrophobicity, microplastics (MPs) tend to act as vectors for various organic pollutants. However, in contrast to well-studied pollutants like polycyclic aromatic hydrocarbons, the sorption of benzene-series compounds on MPs has been seldom studied. To investigate the sorption process, the isotherms were determined for the sorption of three benzene-series sorbates by three polymers with different physicochemical properties. The linear sorption isotherms observed for PE indicate that sorbate uptake was dominated by partitioning into the bulk polymer. In contrast, the non-linear isotherms of PP and PVC imply that adsorption onto surfaces was the dominant mechanism. Sorption capacity of m-xylene and ethylbenzene increased in the following order: polyvinyl chloride (PVC) < polyethylene (PE) < polypropylene (PP). This order does not reflect the polarity or the crystallinity of the investigated MPs, suggesting the influence of additional factors (e.g., glass transition temperature, specific surface area) on the sorption of BTEX by MPs. In addition, the particle size and morphology of MPs are also factors affecting sorption capacity. The strong correlation between the sorption coefficients and sorbate hydrophobicity indicates that the hydrophobic interactions played a crucial role. Meanwhile, specific sorbate properties, such as electronic structure and molecular polarizability, are also significant factors that affect the sorption behaviors.