S11: Microbial biodefluorination of polyfluorinated chemicals in the environment

Perfluoroalkyl sulfonates (PFASs) and carboxylates (PFCAs) are widely detected in the environment due to their broad and historical applications.  The sources of PFASs and PFCAs in the environment may come from direct emissions and indirect precursor degradation.  Potential precursors include perfluoroalkyl sulfonamides, polyfluorinated ethers, and fluorotelomer alcohols [FTOHs, F(CF₂)_nCH₂CH₂OH, n = 4, 6, 8, 10].  The 6:2 and 8:2 FTOHs are major raw materials used to manufacture FTOH-based products for industrial and consumer applications.  Understand of the enzyme-catalyzed microbial biodefluorination of polyfluorinated chemicals is essential for identifying microbes and suitable conditions to degrade persistent products of FTOHs released to the environment. 

In recent years, evidences show that multiple –CF₂– groups within 6:2 and 8:2 FTOHs can be removed via enzymatic defluorination to form shorter-chain PFCAs [F(CF₂)_nCOOH, n = 3,4,5,7]   and  x:3 acids [F(CF₂)_xCH₂CH₂COOH, x = 3,4,5,7].  For example, one –CF₂– was removed from 5:3 acid [F(CF₂)₅CH₂CH₂COOH] via 7 enzymatic steps to form 4:3 acid, which can be further degraded to 3:3 acid by removing additional –CF₂– via the same enzymatic steps.  However, the biodefluorination steps involved in degrading 6:2 FTOH to PFPeA [F(CF₂)₄COOH] and from 8:2 FTOH to PFHxA [F(CF₂)₅COOH] are still not understood.  Furthermore, it is still unknown what enzymes are responsible for the biodefluorination and partial mineralization of FTOHs and 5:3 and 4:3 acids.  Current understanding of microbial defluorination of polyfluorinated chemical offers opportunity to further study both aerobic and anaerobic biodefluorination mechanisms for future microbial remediation strategies to degrade poly- and per-fluorinated alkyl acids in the environment.