When fed glycerol, naturally occurring bacteria in mine water converted 95% of dissolved uranium into a surprisingly stable compound that resists re-entering the water.
Uranium is a radioactive heavy metal typically locked inside minerals in soil. But mining and other environmental processes can change uranium into forms that dissolve in water, allowing it to spread through the environment and create problems because of its toxicity.
Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), working with Wismut GmbH and the University of Granada, have now shown for the first time that bacteria can transform dissolved uranium into a stable chemical compound when glycerol is available as a food source. The findings were published in Nature Communications.
Bacteria found in soil and water are essential parts of natural ecosystems, and some species can process substances harmful to humans. The team collected mine water from a flooded uranium mine in the Ore Mountains and added glycerol to samples kept in an oxygen-free environment — mimicking natural conditions at depths of approximately 2,000 meters.
Over time, the bacteria consumed the glycerol and began accumulating uranium in their cell walls. After 130 days, only about five percent of the uranium remained dissolved in the water.
The researchers then examined the bacterial membranes using advanced microscopy and spectroscopy at the European Synchrotron Radiation Facility in Grenoble. They discovered that the bacteria had converted the uranium into an unusual pentavalent form — a chemical state that had been considered rare and unstable. The pentavalent uranium combined with iron and oxygen to form FeU(V)O4, a compound that remains stable even when exposed to atmospheric oxygen.
This same compound was first identified in 2020 in soil samples from Croatia contaminated by uranium ammunition, where it had remained stable for more than 25 years. But until now, scientists did not know how it formed in nature or that bacteria played a role in its creation.
The discovery opens new possibilities for bioremediation — using living organisms to clean up contaminated environments. If researchers can better understand the biochemical and geochemical processes that make this transformation possible, bacteria could one day be deployed to treat uranium-contaminated water at mining sites and other locations.
The team plans to study uranium-binding bacteria in greater detail and investigate the mechanisms behind the transformation. The finding is particularly significant because dissolved uranium is highly mobile in water, while the stable mineral form is far less likely to spread.