Bacterial Desulfonation and Defluorination of 6:2 Fluorotelomer Sulfonate (6:2 FTS)
Abstract
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.
Citation
Shi, Ying (2018). Bacterial Desulfonation and Defluorination of 6:2 Fluorotelomer Sulfonate (6:2 FTS). Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192044.