Delving into the most bizarre biogeochemical cycles: the role of fungi in the transformation of rare earth elements

Rare elements are indispensable in the manufacturing of high-tech products, including smartphones, computer electronic components and screens. Due to their high demand, they are intensively mined, severely impacting ecosystems and geopolitical equilibria. Their recovery from waste is still poorly considered, but would represent an economically attractive solution. Fungal geomicrobiological traits could provide innovative, sustainable and nature-inspired solutions in this complex scenario. Fungi play a crucial role in the cycling of most elements and can tolerate high concentrations of toxic compounds [1]. They can bioaccumulate and transform these compounds through direct or indirect mechanisms, which include the production of specific metabolites (e.g., organic acids and siderophores). Among the least investigated elements for their interaction with fungi are the metals Gallium(Ga), Indium(In) and Yttrium(Y), and the metalloid Germanium(Ge) [2]. Very little is known about their effects on fungal metabolism, and there are no comprehensive studies on their possible positive or negative metabolic role. Tests on fungal behaviour (24 strains) in the presence of these elements were conducted on solid media with the elements'oxides, assessing tolerance based on mycelial weight and colony area. Variations in media pH and secondary biomineral precipitation were evaluated. A modified microculture system, enabling multimodal imaging and SEM-EDS analysis, was used to investigate fungal assimilation and transport of elements through hyphae, as well as biomineral precipitation [3]. Eleven of the tested strains determined an acidification of the medium pH, while the other 13 either did not modify or increased the pH compared to the chemical control. In several strains, Ge and In interfered with the medium pH modification that occurred due to growth, either reducing their acidification ability or inducing a pH increase. The results [4] revealed that each strain exhibited specific mechanisms for interacting with the elements, along with varying degrees of tolerance, bioaccumulation, and biomineralisation.