New Jersey Institute of Tech
Ph.D. Candidate in Environmental Science 2017-present New Jersey Institute of Technology (NJIT), Newark, NJ, USA; B.E. in Environmental Engineering 2013-2017 School of Environment and Resources, Jilin University, China
Substrate-Mediated Biotransformation and Biodefluorination of FTCAs by Actinomycetes
Background/Objectives: Fluorotelomer carboxylic acid (FTCA, e.g. 6:2FTCA and 5:3FTCA), an important precursor of perfluorinated carboxylic acid (PFCA, e.g. PFOA and PFHxA) and an essential metabolic intermediate for biotransformation of various PFASs precursors (e.g. FTS, FTSA, PAP), a raw material of surfactant industry, has been widely detected in the environment, especially in landfill leachate. FTCAs were more toxic than PFCAs and tended to bioaccumulate inside animal bodies. 5:3FTCA was found to be biodegradable by activated sludge. However, the biodefluorination efficiency is not satisfied and biotransformation mechanisms of 6:2FTCA and 5:3FTCA by single strains are understudied. This research focuses on investigating the influence of substrates on aerobic biotransformation pathway and biodefluorination mechanism of 6:2FTCA and 5:3FTCA by four Actinomycetes, including Mycobacterium dioxanotrophicus PH-06, Mycobacterium smegmatis Laboratory Strain MC2-155, Rhodococcus opacus 1CP, and Rhodococcus jostii RHA1.
Approach/Activities: The bacteria were cultured in ammonium mineral salt (AMS) medium with different substrates (ethanol, glucose, succinate, and citrate) and were harvested at the OD of 1.0. The liquid culture was centrifuged and washed three times with Phosphate-buffered saline (PBS) solution before being used. In resting cell experiments, the initial OD was 0.6, with no extra carbon source offered. Liquid phase fluoride concentration was monitored by fluoride electrode while FTCAs and their metabolites were identified and quantified by novel Nano-ESI High-Resolution Mass Spectrometry. All treatments were performed in triplicate, and abiotic controls were conducted using killed cells. Results/Lessons Learned. The defluorination efficiency was changing between different strains feeding with various substrates. Four substrates (e.g.., glucose, ethanol, succinate, and citrate) were used to grow RHA1 culture for 6:2 FTCA metabolism. The initial 6:2FTCA concentration was 40µM. After 48 hours, the highest fluoride concentration of 0.116 mM with 100% 6:2FTCA removal were observed by RHA1 fed with glucose. Similarly, 0.08 mM defluorination was observed by MC2-155 fed with glucose, while only 0.005mM defluorination with 6.9% 6:2FTCA removal was achieved by PH-06 fed with glucose. Also, though known as a robust 1,4-dioxane degrader, growth and degradation activity of PH-06 was completely inhibited by the presence of 6:2 FTCA with its concentration as low as 5.0 mg/L. The defluorination of 5:3FTCA by all four strains was limited (less than 0.001mM). However, the removal of 5:3FTCA reached over 90% by RHA1 and MC2-155 fed with glucose. More than 10 PFASs were detected as the metabolites of 6:2FTCA biotransformation, including but not limited to PFHpA, 6:2FTUCA 5:3FTCA, 5:3Uacid, PFHxA, and PFPeA. However, the mass balance result indicated they were not the major intermediates accounting for the absent of 6:2FTCA. Similarly, no significant increase of traditional 5:3FTCA downstream metabolites were observed. Thus, we are further investigating the novel and major metabolites of biodefluorination by non-targeting HRMS to complete potential FTCAs biotransformation pathways of different bacteria stimulated by different substrates. This research will be of significant value for the development of cost-efficient bioremediation strategies to remove FTCAs contamination with optimized defluorination and minimized accumulation of PFCAs and other persistent compounds.