6:2 Fluorotelomer sulfonic acid (6:2 FTSA, F(CF₂)₆CH₂CH₂SO₃H) is a common and persistent fluorinated compound detected in the environment as it has been widely used in various industries including metal plating, plastics, and fluoropolymers manufacturing, and present in aqueous film-forming foams (AFFFs). Exposure to 6:2 FTSA has been linked to liver and kidney damage in laboratory rat studies. Despite several studies have reported biodegradation of 6:2 FTSA, 6:2 FTSA remains persistent in the environment. Biotransformation of 6:2 FTSA was only observed in the absence of sulfate, not in the presence of sulfate, suggesting that desulfonation was important for 6:2 FTSA biodegradation. However, factors affecting the biotransformation, and enzymes involved desulfonation and defluorination remain poorly understood.
This study identified enzymes involved in 6;2 FTSA desulfonation and defluoriantion and deciphered the effects of carbon and sulfur sources on their expression in a well-characterized bacteria strain Rhodococcus jostii RHA1(designated as RHA1 hereafter). Under sulfur-rich conditions, butanol-grown RHA1 could defluorinate 6:2 FTOH (F(CF₂)₆CH₂CH₂OH) but not 6:2 FTSA, suggesting that the sulfonate group in 6:2 FTSA might hinders enzymatic defluorination. Several desulfonating and defluorinating enzymes in RHA1 were identified and their roles in biotransformation of 6:2 FTSA were confirmed. Effects of carbon and sulfur sources on the expression levels of these enzymes were delineated. New biotransformation metabolites of 6:2 FTSA were also detected and used to propose a degradation pathway. Our results suggested that the genes encoding these desulfonating and defluorinating enzymes can be used as potential markers to assess 6:2 FTSA biotransformation in the environment, and fill a critical knowledge gap in the biotransformation of 6:2 FTSA.

Mark Strynar

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