This project will develop the scientific basis to allow for future applications of biological or coupled chemical-biological treatment processes to cost-effectively remove fluorotelomers and perfluorooctane sulfonate (PFOS) from subsurface environments. The specific objectives are to: (1) elucidate the mechanisms of bacterial desulfonation and metabolism of fluorotelomer sulfonates and sulfonamide derivatives at the genetic and biochemical levels; (2) improve understanding of step-wise microbial defluorination processes that lead to complete defluorination of fluorotelomers and characterize bacterial consortia and functional genes involved; and (3) develop an understanding of synergistic photochemical reduction and anaerobic microbial defluorination processes that degrade PFOS.

Building upon preliminary data in PFAS biotransformation, the hypothesis is that fluorotelomers can be mineralized by microorganisms. To enable complete defluorination, knowledge of the microbial desulfonation process and “one-carbon removal pathways” that are common to fluorotelomers will be advanced.

Task 1 is based on previous work where the enzymes involved in C-S and C-F bond cleavages of 6:2 fluorotelomer sulfonate (6:2 FTSA) and its sulfonamide betaine derivative by the soil bacterium Gordonia NB4-1Y were tentatively proposed. Task 1 will elucidate mechanisms of C-S and C-F bond cleavage at genetic and biochemical levels. Proteomics and transcriptomics will be used to identify proteins involved in fluorotelomer compound metabolism, followed by computational biology and crystallography to identify structural features that allow the identified enzymes to interact with fluorinated substrates. The enzymes involved in defluorination of 6:2 FTSA will be identified and enzyme-PFAS adducts will be characterized.

Task 2 is built on previous work in which unacclimated microbial communities use “one-carbon removal pathways” to partially mineralize various fluorotelomers. Task 2 will characterize bacterial consortia and functional genes involved in the step-wise defluorination processes. Various enrichment methods will be used to cultivate pure and mixed bacterial cultures capable of extensive or complete defluorination, and a culture-independent technique (DNA-Stable Isotope Probing) will be applied to identify specific microorganisms that incorporate carbon from fluorotelomers into biomass. Phylogenetic, metabolic, and genomic characterization of the most promising bacterial isolates and consortia will be performed.

Given what is known about fluorotelomers, biological dehalogenation, and dehalorespiration reactions, Task 3 will examine the possibility that partial defluorination products of PFOS might be further broken down by microorganisms. Photochemical reduction of PFOS will be performed and the by-products will be exposed to anaerobes in the presence of redox mediators. The reactions will be chemically profiled, and the ecotoxicity of terminal products assessed. The two-step chemical-biological process will be applied to water from contaminated sites for proof-of-concept.

This research will reduce DoD liabilities by establishing fundamental understanding of the microorganisms, genetics, and biochemistry involved in biological C-S and C-F cleavage. The knowledge will guide development of cost-effective biological treatment strategies in the long-term, while in the short-term will provide bacterial genetic markers for assessing the natural attenuation potential of microbial communities at DoD sites, monitoring the activity of those communities, and addressing site limitations inhibiting biological PFAS removal. (Anticipated Project Completion - 2024)