Rob Schmitz (Delft University of Technology)

Summary of presentation:
Rare earth elements (REEs), 17 metals including the lanthanides, scandium, and yttrium, are vital to technologies like electric vehicles, wind turbines, and medical imaging. Gadolinium (64Gd), in chelated form widely used in the MRI contrast agent gadoteric acid, is excreted through urine after use. Wastewater systems cannot effectively recycle it, while gadolinium mining creates considerable environmental strain. Fascinatingly, some bacteria take up REEs from the environment (1). Applying bacteria and their proteins can advance selective and more sustainable recycling of REEs like Gd, yet this emerging field remains largely underexplored.

We engineered and produced the highly specific lanthanide-binding protein Lanmodulin (LanM) from the phyllosphere-inhabiting Methylorubrum extorquens in E. coli cells. Hereafter, we purified LanM through heat purification and ion exchange chromatography and immobilized it on beads using covalent interactions. We reveal that Gd3+-ions can be recovered from gadoteric acid through an acid-based pre-treatment and subsequently bound to LanM with 95 ± 3 % efficiency. The engineered LanM remains functioning at a pH as low as 2.5, and Gd3+-ions can be recovered from LanM through mild acid treatment. Other cations present in urine (e.g., Na+, K+ and Ca2+) do not bind to LanM, enabling selective Gd recovery.

Together, our results show how an engineered bacterial protein can be heterologously expressed through heat purification and efficiently recover gadolinium ions to recovery this precious from waste streams.