6:2 fluorotelomer sulfonic acid (6:2 FTSA) is one of per- and poly-fluoroalkyl substances that has been widely used in industries and as a key ingredient in aqueous film-forming foams (AFFF). The widespread of 6:2 FTSA in the environment have raised the public attentions and concerns. While biotransformation pathway of 6:2 FTSA has been reported, factors affecting desulfonation and defluorination of 6:2 FTSA remain poorly understood. Moreover, current knowledge on phytoremediation and the role of rhizobacteria on 6:2 FTSA biotransformation is limited. To fill the knowledge gap, the goal of this research to elucidate factors that affect the biotransformation and uptake 6:2 FTSA in phyto/rhizoremediation. The effects of carbon and sulfur sources on the gene expression of Rhodococcus jostii RHA1 which is responsible for the 6:2 FTSA biotransformation were first investigated. While alkane monooxygenase and cytochrome P450 were highly expressed in ethanol-, 1-butanol-, and n-octane-grown RHA1 in sulfur-rich medium, these cultures only defluorinated 6:2 fluorotelomer alcohol (6:2 FTOH) but not 6:2 FTSA, suggesting that the sulfonate group in 6:2 FTSA hinders enzymatic defluorination. In sulfur-free growth media, alkanesulfonate monooxygenase was linked to desulfonation of 6:2 FTSA; while alkane monooxygenase, haloacid dehalogenase, and cytochrome P450 were linked to defluorination of 6:2 FTSA. Four degradation metabolites were confirmed, and one was identified as a tentative metabolite. The potential of phytoremediation for 6:2 FTSA by a model plant Arabidopsis thaliana coupled with bioaugmentation of RHA1 under different nutrient and microbiome conditions were then investigated. A hyperaccumulation of 6:2 FTSA, defined as tissue/soil concentration > 10 and high translocation factor (TF > 3), was observed in plants. However, biotransformation of 6:2 FTSA only occurred under sulfur-limited conditions. Spiking RHA1 enhanced the biotransformation of 6:2 FTSA in soil and promoted plant growth. Soil microbiome analysis uncovered Rhodococcus as one of the dominant species in all RHA1 spiked soil. Different nutrients, including sulfur and carbon, bioaugmentation, and 6:2 FTSA conditions significantly shift the composition of the microbial community. The effects of root exudates grown under different nutrient conditions and bioaugmentation of RHA1 on biotransformation of 6:2 FTOH were investigated. Spiking root exudates enhanced the 6:2 FTOH biotransformation in soil microcosms. Interestingly, higher humic-like and protein-like substance in the root exudates linked to higher defluorination of 6:2 FTOH. Presence of RHA1 and root exudates facilitates 6:2 FTOH transformation resulting in formation of diverse metabolites. Microbial community analysis revealed that Rhodococcus was predominant in all RHA1 spiked treatments. The presence of different root exudates changed the diversity and the composition of microbial communities. 13C stable isotope probing (SIP) were applied to identify the active 6:2 FTSA degrader in the rhizosphere of Arabidopsis thaliana. SIP revealed that the known 6:2 FTOH/6:2 FTSA degrader Pseudomonas was the most predominant active rhizosphere bacteria. However, the spiked RHA1 was less competitive in rhizosphere soil compared to bulk soil. Carbon source or AFFF-surfactant is an important driver cause the shifting of microbial composition.
