Radioactive Elements Replace Basic Rare Earth Metals – ScienceDaily

In addition to being a useful material in all kinds of major technologies, lanthanides are important to bacteria, which use rare earth metals in their metabolism. However, it turns out that they are not as indispensable as previously thought, as an international interdisciplinary team led by Professor Lena Doman of the Department of Chemistry at LMU has shown: some bacteria can use the radioactive elements americium and curium instead of – and sometimes even prefer – the lanthanides.

Bacteria that use lanthanides circulate 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 the lanthanides and incorporate them into an important metabolic enzyme, the lanthanide-dependent methanol dehydrogenase. The two members of the radioactive actinides, americium and curium, are very similar to the lanthanides when it comes to key chemical properties such as size and charge. “So we asked ourselves if bacteria could use actinides in place of their basic lanthanides,” Doman says.

Now researchers have proven that this is indeed the case. They have performed an in vivo study of two methylotrophic bacterial strains in collaboration with the Helmholtz Center Dresden-Rossendorf (HZDR). “We fed the microbes various elements and showed that they contain americium and curium and also grow with these elements,” Doman explains. It is important that the actinides have the same oxidation state and are of the same size as the normally used lanthanides, so that they fit into the active center of methanol dehydrogenase. Additional in vitro studies using isolated methanol dehydrogenase also show that the enzyme works with actinides and displays similar activities.

“We can thus show for the first time that organisms can use these radioactive elements in life processes,” Doman asserts. When bacteria were shown a mixture of different lanthanides and actinides, they preferred americium and curium over some of the lanthanides. The bacteria’s ability to incorporate radioactive actinides is interesting in terms of potential applications: “Methylotrophic bacteria can be used in bioremediation or in the separation and recycling of lanthanides and actinides. Such mixtures that are difficult to separate are often found in nuclear fuel,” says Doman.