Year: 2018
Type: dissertation
Abstract: 6:2 Fluorotelomer sulfonate (6:2 FTS) is an emerging environmental\ncontaminant. As a transformation product from the degradation of formulant in the\naqueous film-forming foams (AFFF), 6:2 FTS has been frequently found with high\nconcentrations in groundwater and soil, especially those adjacent to firefighting training\nareas. Due to its wide occurrence, toxicity, and bioaccumulation potential, 6:2 FTS has\nreceived a lot of attentions in the past decade. Conflicting biodegradability of 6:2 FTS\nunder aerobic conditions were observed in activated sludge and river sediment. There\nwas no evidence of biodegradation or biotransformation of 6:2 FTS occurring under\nanaerobic conditions.\nCurrent knowledge on the factors determining biotransfomation and\nbiodefluorination rate of 6:2 FTS is still unclear. To bridge this knowledge gap, this\nthesis characterized cultivable 6:2 FTS-degrading strains and elucidated the rate-limiting\nstep affecting biotransfomation and biodefluorination of 6:2 FTS, with an emphasis on\nenzymes responsible for desulfonation. Two desulfonating enzyme systems, taurine\ndioxygenase (TauD) and two-component alkanesulfonate monooxygenase (SsuE/D),\nwere examined for their ability to desulfonate 6:2 FTS.\nA rhizosphere soil bacterial isolate, Pseudomonas strain SYC, can not only\nbiotransform but also defluorinate 6:2 FTS. Two 6:2 FTOH-degrading strains,\nRhodococcus jostii RHA1 and Pseudomonas oleovorans, also showed an ability to\ndefluorinate 6:2 FTS. According to the degree of defluorination under different growth\nconditions, 6:2 FTS was readily defluorinated when it served as the sole sulfur source\nwith appropriate carbon source being provided, such as ethanol, 1-butanol, and n-octane.\nThere was no observable fluoride release when sulfate presents in the medium, likely\ndue to the repression of the expression of desulfonating enzymes, suggesting that\ndesulfonation is the first step in 6:2 FTS metabolism by 6:2 FTS-degrading strains.\nThree desulfonating-associated enzymes, taurine dioxygenase (TauD),\nalkanesulfonate reductase (SsuE) and alkanesulfonate monooxygenase (SsuD), were\nsuccessfully expressed and produced by E. coli competent cell BL21 (DE3). Free sulfite\nrelease was observed when using crude extract of enzymes to react with 6:2 FTS,\nindicating successful desulfonation by TauD and SsuE/D system.\nThe elucidations of rate-limiting step of 6:2 FTS defluorination, as well as\nenzymes responsible for 6:2 FTS desulfonation, provide fundamental knowledge for\nfuture studies on the molecular biology of 6:2 FTS metabolism in bacteria and the\ndevelopment of biological treatment strategies for enhanced 6:2 FTS removal.
Author: Ying Shi
Language: English
Subfield: Environmental Chemistry
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3135386480