Microbe battles contaminants

A relatively common soil bacterium may be the secret weapon against one of our nastier classes of pollutants.

In preliminary work, researchers from Princeton University, US, used the bacterium Acidimicrobium A6, collected from a New Jersey wetland, to successfully break down persistent PFAS (Per- and polyfluoroalkyl substances).

Widely used in products from non-stick pans to firefighting foam, PFAS has been accumulating in organisms throughout the food chain over many years. In the US, the Environmental Protection Agency says there is evidence that it is harmful to human health.

Manufacturers are phasing out several versions of PFAS, but the chemicals are long-lived and, because of the strength of their carbon-fluorine bond, difficult to remove from soil and groundwater in conventional ways.

In the recent trials, which are reported in the journal Environmental Science and Technology, a team led by civil and environmental engineer Peter Jaffé removed 60% of PFAS in lab vials over 100 days of observation using Acidimicrobium A6.

Jaffé cautions, however, that more work is needed before reaching a workable treatment. “This is a proof of concept,” he says. “We would like to get the removal higher, and then go and test it in the field.”

Jaffé and colleague Shan Huang began working with Acidimicrobium A6 several years ago when they investigated a phenomenon in which ammonium broke down in acidic, iron-rich soils in New Jersey wetlands and similar locations.

One challenge, they say, is the bacterium’s demand for iron both to grow and eliminate compounds like ammonium, but Jaffé and two then graduate students determined that they could substitute an electrical anode for the iron in lab reactors. 

This allowed them to more easily grow Acidimicrobium A6 and work with it – and presented a possible way to develop reactors for remediation in the absence of iron.

When they sequenced the Acidimicrobium A6 genome, the researchers noticed certain characteristics that opened the possibility that it could be effective in removing PFAS.

To test their hypothesis, they sealed samples of the bacterium in lab containers then tested their ability to break down the compounds in lab reactors.

After 100 days, the researchers stopped the test and determined that the bacteria had removed 60% of the contaminants and released an equivalent amount of fluoride in the process. 

Jaffé says the 100-day period was arbitrary, and that longer incubations might result in more PFAS removal. The researchers also plan to vary conditions in the reactor to find the optimum conditions.

Acidimicrobium A6 thrives in low oxygen, they say, which makes it particularly effective for soil and groundwater remediation and allows it to function without expensive aeration.