Microbes That Digest Persistent Pollutants and Their Harmful Byproducts

The typical approach for dealing with per- and polyfluoroalkyl substances (PFAS) involves capturing and containing them. However, some microbes have the unique ability to dismantle the robust chemical bonds that enable these substances to remain in the environment for extended periods.

Recently, a team from the University at Buffalo has pinpointed a bacterial strain known to break down and convert at least three types of PFAS, with the crucial ability to deal with toxic byproducts formed during this chemical breakdown.

In a study published in this month’s Science of the Total Environment, the researchers found that the bacterium Labrys portucalensis F11 (F11) successfully metabolized over 90% of perfluorooctane sulfonic acid (PFOS) after being exposed for 100 days. PFOS is a well-known and long-lasting PFAS that the U.S. Environmental Protection Agency classified as hazardous just last year.

The F11 strain also significantly reduced two additional types of PFAS after the same exposure period: 58% of 5:3 fluorotelomer carboxylic acid and 21% of 6:2 fluorotelomer sulfonate.

“The chemical bond between carbon and fluorine in PFAS is extremely robust, making it unsuitable for most microbes as an energy source. However, the F11 strain has managed to evolve to remove fluorine and utilize the carbon component,” explains Diana Aga, PhD, the study’s lead author and a distinguished professor at SUNY, as well as the director of the UB RENEW Institute.

Unlike several previous studies of PFAS-degrading bacteria, Aga’s research also considered smaller chain breakdown products, known as metabolites. In some scenarios, F11 even removed fluorine from these byproducts or degraded them to levels that couldn’t be detected.

“Many earlier studies have solely focused on the degradation of PFAS without addressing the formation of metabolites. We not only tracked PFAS byproducts but also discovered that some of them were further degraded by the bacteria,” notes Mindula Wijayahena, the study’s first author and a PhD student in Aga’s lab.

This research received support from the National Institute of Environmental Health Sciences, part of the National Institutes of Health, with collaborators from the Catholic University of Portugal, the University of Pittsburgh, and Waters Corp.

Selective feeders adapt to PFAS

PFAS are a collection of widespread chemicals that have been used since the 1950s in various products, including nonstick cookware and fire-fighting foams.

While these substances are not the preferred choice for any bacteria, some that exist in polluted soil have adapted and evolved to decompose organic contaminants like PFAS, utilizing the carbon as an energy source.

“Bacteria that endure in highly polluted environments likely do so because they’ve adapted to use surrounding chemical pollutants as nutrients,” explains Aga. “Through evolution, certain bacteria have developed mechanisms to transform chemical contaminants into energy, allowing them to thrive despite the pollution.”

The strain used for this research, F11, was taken from the soil of a contaminated industrial site in Portugal. It had previously shown the capability to remove fluorine from pharmaceutical chemicals but had never been tested with PFAS.

Researchers from the Catholic University of Portugal placed the F11 strain in sealed containers containing only PFAS at a concentration of 10,000 micrograms per liter, without any other carbon source. After incubating for periods of 100 to 194 days, the samples were sent to UB for analysis, which showed that F11 had indeed degraded some of the PFAS.

High levels of fluoride ions in these samples confirmed that the F11 bacteria had detached the fluorine atoms, allowing them to metabolize the carbon atoms.

“The carbon-fluorine bond’s strength is what makes PFAS so resistant to breakdown. Thus, the ability to dismantle these compounds is a vital breakthrough. Importantly, F11 was not only reducing PFOS into smaller fragments but also removing the fluorine from these fragments,” Wijayahena remarked.

Some of the residual metabolites still had fluorine, although after 194 days of exposure to PFOS, F11 was successful in removing fluorine from three of the PFOS byproducts.

“It’s essential to note that there may be other metabolites present in these samples that are so small they go undetected by current techniques,” Aga cautioned.

Transforming PFAS into a viable food source

While the UB team considers their research to be a positive initial step, they acknowledge that the F11 strain took 100 days to substantially break down a significant amount of PFAS without other carbon sources available for its use.

Moving forward, the researchers aim to explore ways to prompt F11 to consume PFAS more quickly, even when faced with alternative energy sources that could enhance their growth rate.

“We want to look into the effects of placing other carbon sources alongside PFAS. However, if those sources are too plentiful and easy to break down, the bacteria might not feel the need to target the PFAS at all,” explains Aga. “Our goal is to provide the F11 colonies with enough nutrients to thrive while ensuring they still prioritize converting PFAS into an energy source.”

In the future, F11 could be used to treat PFAS-contaminated water and soil. This may include developing conditions to cultivate the strain within activated sludge at wastewater treatment facilities or potentially injecting the bacteria directly into contaminated soil or groundwater, a method known as bioaugmentation.

“In wastewater-activated sludge systems, introducing a specific strain could speed up the removal of unwanted compounds by enhancing the existing bacterial community in treatment plants,” says Aga. “Bioaugmentation presents a promising solution that hasn’t been fully utilized for PFAS remediation in the environment yet.”