Speciation and spatial distribution of Eu(III) in fungal mycelium.

Europium, as an easy-to-study analog of the trivalent actinides, is of particular importance for studying the behavior of lanthanides and actinides in the environment. Since different soil organisms can influence the migration behavior of these elements, a detailed knowledge of these interaction mechanisms is important. The aim of this study was to investigate the interaction of mycelia of selected wood-inhabiting (S. commune, P. ostreatus, L. tigrinus) and soil-inhabiting fungi (L. naucinus) with Eu(III). In addition to determining the Eu(III) complexes in the sorption solution, the formed Eu(III) fungal species were characterized using scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, chemical microscopy in combination with the time-resolved laser-induced fluorescence spectroscopy. Our data show that S. commune exhibited significantly higher Eu(III) binding capacity in comparison to the other fungi. Depending on fungal strain, the metal was immobilized on the cell surface, in the cell membranes, and within the membranes of various organelles, or in the cytoplasm in some cases. During the bioassociation process two different Eu(III) fungal species were formed in all investigated fungal strain. The phosphate groups of organic ligands were identified as being important functional groups to bind Eu(III) and thus immobilize the metal in the fungal matrix. The information obtained contributes to a better understanding of the role of fungi in migration, removal or retention mechanisms of rare earth elements and trivalent actinides in the environment.

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Declaration of competing interest The authors declare that they have no competing personal and financial interests.