Bacteria: Radioactive elements replace essential rare earth metals

As well as being a useful material in all kinds of key technologies, lanthanides are important for bacteria, which use the rare earth metals in their metabolism. It turns out, however, that they are not as irreplaceable as previously thought, as an international and interdisciplinary team led by Professor Lena Daumann from the Department of Chemistry at LMU has demonstrated: Certain bacteria can use the radioactive elements americium and curium instead of the lanthanides -- and even prefer them sometimes.

Bacteria that use lanthanides are widespread in the environment. They belong to the so-called methylotrophs, which can use methanol or methane as carbon and energy sources. To do this, they take up lanthanides and incorporate them into an important metabolic enzyme, a lanthanide-dependent methanol dehydrogenase. The elements americium and curium, members of the radioactive actinides, are very similar to the lanthanides when it comes to key chemical properties such as size and charge. "And so we asked ourselves whether the bacteria can use actinides instead of their essential lanthanides," says Daumann.

Now the researchers have demonstrated that this is actually the case. They carried out an in-vivo study of two methylotrophic bacterial strains in collaboration with the Helmholtz Center in Dresden-Rossendorf (HZDR). "We fed the microbes various elements and showed that they incorporate americium and curium and grow just as well with these elements," explains Daumann. It is important that the actinides have the same oxidation state and are of a similar size to the lanthanides normally used, so that they fit in the active center of methanol dehydrogenase. Additional in-vitro studies with isolated methanol dehydrogenase also demonstrate that the enzyme works with the actinides and exhibits similar activities.

"We could thus show for the first time that organisms can use these radioactive elements for life processes," emphasizes Daumann. When the bacteria were offered a mixture of various lanthanides and actinides, they even preferred americium and curium ahead of some lanthanides. The ability of the bacteria to incorporate radioactive actinides is also interesting with respect to potential applications: "Methylotrophic bacteria could potentially be used in bioremediation or in the separation and recycling of lanthanides and actinides. Such difficult-to-separate mixtures are often found in spent nuclear fuel," says Daumann.