Biosynthesis of cerium and gadolinium nanoparticles by Pseudomonas putida KT2440 enables sustainable rare earth elements utilization.

Lanthanides (Ln), a group of 15 rare earth elements (REEs), are critical for advanced technologies, although their conventional extraction and processing are environmentally unsustainable. Here, we present a microbial platform based on Pseudomonas putida KT2440 for the eco-friendly recovery and transformation of Ln, introducing a key methodological innovation: the use of a resting cell system to circumvent the pervasive issue of abiotic lanthanide-phosphate precipitation. This approach enables controlled investigation of Ln biomineralization under mild conditions. Mechanistically, the results showed that Ln recovery proceeds via rapid cell-surface adsorption, followed by surface-templated nucleation and extracellular mineralization. This process leads to the formation of well-defined biogenic nanoparticles primary identified as CePO₄ and GdPO₄. Structural analyses reveal nanorod morphologies, while functional characterization shows that CePO₄ nanoparticles retain photoluminescent properties and GdPO₄ nanoparticles preserve paramagnetic behavior. Compared to conventional chemical synthesis, this biosynthetic strategy eliminates toxic reagents and energy-intensive steps, yielding biocompatible materials with controlled size and morphology. Our findings establish P. putida KT2440 as an efficient and sustainable platform for Ln recovery and functional nanoparticle production, providing a foundation for scalable green alternatives to traditional Ln processing.