October 11, 2024
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Searching for Microbes to Break Down “Forever Chemicals”
Bacteria can degrade particularly harsh varieties of PFAS
A group of bacteria has been shown to be adept at destroying the ultra-tough carbon-fluorine bonds that give the “forever chemicals” their name. This finding raises hopes that microbes will one day help remove these known pollutants from the environment.
Almost 15,000 common chemicals found in everyday consumer products such as pizza boxes, raincoats and sunscreen are recognized as perfluoroalkyl and polyfluoroalkyl substances, or PFASs. These chemicals can enter the body through drinking water or crops fertilized with sludge, and have already infiltrated the bloodstream of almost everyone in the U.S. Scientists have linked low levels of chronic PFAS exposure to a variety of health effects, such as kidney cancer, thyroid disease. and ulcerative colitis.
Current methods for destroying PFAS require extreme heat or pressure, and only work safely with filtered waste. Researchers have long wondered if bacteria could break down chemicals in the natural environment, providing a cheaper and more scalable approach. But carbon-fluorine bonds occur primarily in man-made materials, and PFASs have not been around long enough for bacteria to specifically develop the ability to digest them. The new study — while not the first to identify a microbe that destroys carbon and fluorine bonds — is a step forward, says Northwestern University chemist William Dichtel, who studies energy-efficient ways to chemically degrade PFASs.
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To identify a promising group of bacteria, the study authors analyzed various microbial communities living in wastewater. The four tensions Acetobacterium gender stood out, the group reported in the year Science Advances. Each strain produced an enzyme that can digest caffeate, a natural plant compound that resembles some PFASs. This enzyme replaced some of the fluorine atoms in the PFASs with hydrogen atoms; a “transporter protein” then carried fluoride ion byproducts out of the single-celled microbes, protecting them from damage. Over the course of three weeks, most strains have broken down the targeted PFAS molecules into smaller pieces that can be more easily degraded by traditional chemical means.
Directly targeting carbon-fluorine bonds, Acetobacterium bacteria partially digested perfluoroalkyls, a type of PFAS that few microbes can break down. However, these Acetobacterium strains could only work on perfluoroalkyl molecules with carbon-carbon double bonds next to carbon-fluorine. These “unsaturated” perfluoroalkyl compounds serve as building blocks for larger PFASs; they are produced by chemical manufacturers and are also produced when PFASs are destroyed by incineration.
Scientists had previously demonstrated that a microbe called it Microbial acid sp. Strain A6 can break carbon-fluoro bonds and completely degrade two ubiquitous perfluoroalkyls. This microbe grows slowly, however, and requires strict environmental conditions to function. And researchers still don’t fully understand how this bacterial strain does its job.
The Acetobacterium lines target a separate group of PFASs, and the team hopes to engineer the microbes to improve their effectiveness or expand their reach, potentially yielding more perfluoroalkyls. Lead study author Yujie Men of the University of California, Riverside, imagines that microbes would work better when combined with other approaches to degrade PFASs. The range of chemical structures of these compounds means that “no single laboratory can solve this problem.”
Future commercial use of the microbes would face many hurdles, including breakdown speed and replicability outside the lab, but Men looks forward to seeing how far his team can take the technique. “We are paving the way as we go,” he laughs.
