Deep underground in Germany's Ore Mountains, tiny bacteria are doing something scientists never expected: they are transforming a toxic heavy metal into something harmless that can last for decades.
A team of researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), working with scientists from Wismut GmbH and the University of Granada in Spain, has shown for the first time that bacteria can remove nearly all dissolved uranium from water in just 130 days. When the researchers added glycerol—a simple compound found in plant and animal fats—to mine water samples collected from a flooded uranium mine about 2,000 meters deep, the bacteria got to work. After 130 days, only about 5 percent of the uranium dissolved in the water remained.
"We wanted to create natural conditions for the bacterial community already existing in the mine water because, at that depth, there is usually little or no oxygen," explained Antonio M. Newman-Portela, a former doctoral candidate at HZDR and the University of Granada, and the study's lead author. The bacteria consumed the glycerol and, in the process, pulled the uranium into their cell walls.
But the real surprise came when the scientists examined exactly what chemical forms the uranium had taken. Using powerful X-ray equipment at the European Synchrotron Radiation Facility in Grenoble, France, they discovered the bacteria had converted the uranium into a rare form called pentavalent uranium—chemical shorthand U(V). This type of uranium had previously been seen only as a fleeting, unstable state that disappears quickly.
Even more remarkably, the pentavalent uranium combined with iron and oxygen to form a compound called FeU(V)O4. This substance has no common name yet because scientists only confirmed its existence in 2020, when it was found in soil samples from Croatia. What makes the new discovery extraordinary is that this compound proved incredibly stable—remaining unchanged for more than 25 years, even when exposed to ordinary air.
"Our study has revealed for the first time that bacteria supplied with glycerol as a carbon source can convert toxic uranium dissolved in water," said Dr. Evelyn Krawczyk-Bärsch, a microbiology researcher at HZDR and co-author of the study. The findings, published in the journal Nature Communications, suggest that certain bacteria could eventually help clean up radioactive contamination at old mining sites or nuclear facilities.
The implications are significant. Traditional methods of removing uranium from water can be expensive and require harsh chemicals. But if naturally occurring bacteria can do the job using nothing more than a food source already found in nature, that opens up entirely new possibilities for environmental cleanup. The researchers now plan to investigate whether this process works equally well in different types of soil and water, moving closer to real-world applications that could help restore ecosystems damaged by uranium pollution.