Radioactive elements curium and americium support methylotrophic bacterial life

The biological relevance of early lanthanides, such as neodymium, remained undiscovered until methylotrophic bacteria with lanthanide-dependent metabolism were identified. The respective strains incorporate these elements into the active site of their key metabolic enzyme methanol dehydrogenase (MDH). Growth studies with the strictly lanthanide-dependent thermoacidophile Methylacidiphilum fumariolicum SolV and the mesophilic Methylorubrum extorquens AM1 ΔmxaF mutant demonstrate that the trivalent actinides americium and curium support growth in the absence of the essential lanthanides. In fact, the bacteria make no distinction between lanthanide and actinide ions if they have the correct size and oxidation state. Time-resolved laser-induced fluorescence spectroscopy, liquid scintillation counting, and inductively coupled plasma mass spectrometry confirm the bacterial uptake. The interchangeability of f-block elements is supported by very similar enzymatic activities of recombinant methanol dehydrogenase reconstituted with different metal ions. Our combined in vivo and in vitro results firmly establish that actinides support growth of methylotrophic bacteria, suggesting a potential biological role for these radioactive elements. Importantly, bacteria capable of utilizing actinides will also be able to mobilize these elements in the environment. This may lead to applications for bioremediation and recycling/separation of lanthanides and actinides.