Bacteria living deep inside a flooded former uranium mine in eastern Germany have been found capable of locking dissolved, toxic uranium into an unusually stable form, according to new research from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The discovery, made in collaboration with Wismut GmbH and the University of Granada in Spain, points to a possible low-cost route for treating contaminated water at old mining sites across Europe.
The study focused on the Schlema-Alberoda mine in the Ore Mountains of Saxony, once part of the vast Wismut uranium mining complex that supplied the Soviet nuclear programme during the Cold War. Between 1946 and 1990, the Soviet-German Wismut company extracted 231,000 tonnes of uranium ore in the region, making it the world's third-largest producer at the time. Since German reunification, Wismut GmbH has managed the long, costly task of decommissioning and rehabilitating the mines, several of which have flooded and continue to release uranium-contaminated groundwater that requires ongoing treatment.
Feeding the microbes that were already there
Rather than introducing new organisms, the HZDR team worked with the microbial community naturally present in the mine water, an environment deep underground with little oxygen. They added glycerol, a simple compound also found in fats, as a food source to stimulate the bacteria's metabolism.
The effect was striking. Researchers demonstrated for the first time that bacteria can convert uranium dissolved in water into a stable chemical compound when supplied with glycerol as a food source, phys.org reported. Nature World News, another outlet that reviewed the underlying Nature Communications paper, reported that bacteria removed about 95% of dissolved uranium from contaminated mine water in 130 days, transforming it into a more stable compound.
“"Our study has revealed for the first time that bacteria supplied with glycerol as a carbon source can convert toxic uranium dissolved in water into a stable chemical compound," said Dr. Evelyn Krawczyk-Bärsch, a scientist in HZDR's Terrestrial Microbiology research group and co-author of the study.”
A rare chemical state, made durable
Uranium typically exists in a valency, or electron-bonding state, of four or six. The pentavalent form, with a valency of five, is chemically rare and normally short-lived. The researchers found that the bacteria helped uranium settle into this pentavalent state and combine with iron and oxygen to form a compound called FeU(V)O4, a substance so new it does not yet have a common name.
Even more unexpectedly, drying the bacterial biomass and exposing it to oxygen did not break the compound down. Instead, according to reporting on the study, the amount of FeU(V)O4 increased when the dried biomass was exposed to air, suggesting oxygen helped stabilise rather than destroy the uranium mineral. This runs counter to the usual assumption that oxygen tends to remobilise uranium by converting it back into a soluble form.
Why it matters beyond one German mine
Uranium contamination is notoriously difficult to manage because the metal readily changes chemical form, moving through groundwater when soluble and settling into rock when locked into minerals. The current approach at Schlema-Alberoda, and at similar sites, relies on continuously pumping, aerating, chemically treating and filtering water, a process that generates large volumes of contaminated sludge needing long-term storage.
A biological alternative that uses the site's own microbial life, rather than chemical dosing, could in principle be cheaper and more sustainable. But the researchers themselves caution that important questions remain unanswered, including how much glycerol would be needed at full mine scale, how it would be distributed through kilometres of flooded tunnels, and whether the uranium compound could remobilise if conditions change, for instance if the mine floods with oxygen-rich rainwater.
For Europe, where legacy uranium and other heavy-metal mining sites remain scattered across Germany, the Czech Republic and elsewhere in the former Eastern Bloc, the findings offer an early but genuine proof of principle rather than a ready-made solution. The team's next work will test whether the process can be controlled and scaled outside laboratory conditions, and whether similar microbial communities exist at other contaminated sites.
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