6:2 Fluorotelomer sulfonate (6:2 FTS) is an emerging environmental contaminant. As a transformation product from the degradation of formulant in the aqueous film-forming foams (AFFF), 6:2 FTS has been frequently found with high concentrations in groundwater and soil, especially those adjacent to firefighting training areas. Due to its wide occurrence, toxicity, and bioaccumulation potential, 6:2 FTS has received a lot of attentions in the past decade. Conflicting biodegradability of 6:2 FTS under aerobic conditions were observed in activated sludge and river sediment. There was no evidence of biodegradation or biotransformation of 6:2 FTS occurring under anaerobic conditions. Current knowledge on the factors determining biotransfomation and biodefluorination rate of 6:2 FTS is still unclear. To bridge this knowledge gap, this thesis characterized cultivable 6:2 FTS-degrading strains and elucidated the rate-limiting step affecting biotransfomation and biodefluorination of 6:2 FTS, with an emphasis on enzymes responsible for desulfonation. Two desulfonating enzyme systems, taurine dioxygenase (TauD) and two-component alkanesulfonate monooxygenase (SsuE/D), were examined for their ability to desulfonate 6:2 FTS. A rhizosphere soil bacterial isolate, Pseudomonas strain SYC, can not only biotransform but also defluorinate 6:2 FTS. Two 6:2 FTOH-degrading strains, Rhodococcus jostii RHA1 and Pseudomonas oleovorans, also showed an ability to defluorinate 6:2 FTS. According to the degree of defluorination under different growth conditions, 6:2 FTS was readily defluorinated when it served as the sole sulfur source with appropriate carbon source being provided, such as ethanol, 1-butanol, and n-octane. There was no observable fluoride release when sulfate presents in the medium, likely due to the repression of the expression of desulfonating enzymes, suggesting that desulfonation is the first step in 6:2 FTS metabolism by 6:2 FTS-degrading strains. Three desulfonating-associated enzymes, taurine dioxygenase (TauD), alkanesulfonate reductase (SsuE) and alkanesulfonate monooxygenase (SsuD), were successfully expressed and produced by E. coli competent cell BL21 (DE3). Free sulfite release was observed when using crude extract of enzymes to react with 6:2 FTS, indicating successful desulfonation by TauD and SsuE/D system. The elucidations of rate-limiting step of 6:2 FTS defluorination, as well as enzymes responsible for 6:2 FTS desulfonation, provide fundamental knowledge for future studies on the molecular biology of 6:2 FTS metabolism in bacteria and the development of biological treatment strategies for enhanced 6:2 FTS removal.
