High Persistence of Novel Polyfluoroalkyl Betaines in Aerobic Soils.

Some contemporary aqueous film-forming foams (AFFFs) contain n:3 and n:1:2 fluorotelomer betaines (FTBs), which are often detected at sites impacted by AFFFs. As new chemical replacements, little is known about their environmental fate. For the first time, we investigated the biotransformation potential of 5:3 and 5:1:2 FTBs and a commercial AFFF that mainly contains n:3 and n:1:2 FTBs (n = 5, 7, 9, 11, and 13). Although some polyfluoroalkyl compounds are precursors to perfluoroalkyl acids, 5:3 and 5:1:2 FTBs exhibited high persistence, with no significant changes even after 120 days of incubation. While the degradation of 5:3 FTB into suspected products such as fluorotelomer acids or perfluoroalkyl carboxylic acids (PFCAs) could not be conclusively confirmed, we did identify a potential biotransformation product, 5:3 fluorotelomer methylamine. Similarly, 5:1:2 FTB did not break down or produce short-chain hydrogen-substituted polyfluoroalkyl acids (n:2 H-FTCA), hydrogen-substituted PFCA (2H-PFCA), or any other products. Incubating the AFFF in four soils with differing properties and microbial communities resulted in 0.023-0.25 mol % PFCAs by day 120. Most of the products are believed to be derived from n:2 fluorotelomers, minor components of the AFFF. Therefore, the findings of the study cannot be fully explained by the current understanding of structure-biodegradability relationships.

Transcriptomic response of Gordonia sp. strain NB4-1Y when provided with 6:2 fluorotelomer sulfonamidoalkyl betaine or 6:2 fluorotelomer sulfonate as sole sulfur source.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are environmental contaminants of concern. We previously described biodegradation of two PFAS that represent components and transformation products of aqueous film-forming foams (AFFF), 6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB) and 6:2 fluorotelomer sulfonate (6:2 FTSA), by Gordonia sp. strain NB4-1Y. To identify genes involved in the breakdown of these compounds, the transcriptomic response of NB4-1Y was examined when grown on 6:2 FTAB, 6:2 FTSA, a non-fluorinated analog of 6:2 FTSA (1-octanesulfonate), or MgSO4, as sole sulfur source. Differentially expressed genes were identified as those with ± 1.5 log2-fold-differences (± 1.5 log2FD) in transcript abundances in pairwise comparisons. Transcriptomes of cells grown on 6:2 FTAB and 6:2 FTSA were most similar (7.9% of genes expressed ± 1.5 log2FD); however, several genes that were expressed in greater abundance in 6:2 FTAB treated cells compared to 6:2 FTSA treated cells were noted for their potential role in carbon-nitrogen bond cleavage in 6:2 FTAB. Responses to sulfur limitation were observed in 6:2 FTAB, 6:2 FTSA, and 1-octanesulfonate treatments, as 20 genes relating to global sulfate stress response were more highly expressed under these conditions compared to the MgSO4 treatment. More highly expressed oxygenase genes in 6:2 FTAB, 6:2 FTSA, and 1-octanesulfonate treatments were found to code for proteins with lower percent sulfur-containing amino acids compared to both the total proteome and to oxygenases showing decreased expression. This work identifies genetic targets for further characterization and will inform studies aimed at evaluating the biodegradation potential of environmental samples through applied genomics.

Degradation and defluorination of 6:2 fluorotelomer sulfonamidoalkyl betaine and 6:2 fluorotelomer sulfonate by Gordonia sp. strain NB4-1Y under sulfur-limiting conditions.

6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB) is a major component of aqueous film-forming foams (AFFFs) used for firefighting and is frequently detected, along with one of its suspected transformation products, 6:2 fluorotelomer sulfonate (6:2 FTSA), in terrestrial and aquatic ecosystems impacted by AFFF usage. Biochemical processes underlying bacterial biodegradation of these compounds remain poorly understood due to a lack of pure culture studies. Here, we characterized the water-soluble and volatile breakdown products of 6:2 FTSA and 6:2 FTAB produced using Gordonia sp. strain NB4-1Y cultures over seven days under sulfur-limited conditions. After 168 h, 99.9% of 60 µM 6:2 FTSA was degraded into ten major breakdown products, with a mol% recovery of 88.2, while 70.4% of 60 µM 6:2 FTAB was degraded into ten major breakdown products, with a mol% recovery of 84.7. NB4-1Y uses two pathways for 6:2 FTSA metabolism, with 55 mol% of breakdown products assigned to a major pathway and <1.0 mol% assigned to a minor pathway. This work indicates that rapid transformation of 6:2 FTSA and 6:2 FTAB can be achieved under controlled conditions and improves the bacterial metabolism of these compounds.