Abstract

Rare-earth elements (REEs) are crucial metals with limited global availability due to their indispensable role in various high-tech industries. As the demand for rare-earth elements continues to rise, there is a pressing need to develop sustainable methods for their recovery from secondary sources. Focusing on Exiguobacterium sp. SH31, this research investigates the impact of La, Eu, Gd, and Sm on its physiological performance and biosorption capacity. Tolerance was assessed at pHpzc from 7 to 8 with up to 1 mM rare-earth element concentrations. This study visualized the production of extracellular polymeric substances using Congo red assays and quantified them with ultraviolet-visible spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy characterized the functional groups involved in metal interactions. The SH31 strain displayed significant rare-earth element tolerance, confirmed extracellular polymeric substance (EPS) production under all conditions, and increased production in the presence of Sm. Spectroscopy analysis revealed changes in wavelengths associated with OH and R-COO-, suggesting rare-earth element interactions. SH31 demonstrated efficient metal adsorption, with removal rates exceeding 75% at pHpzc 7 and over 95% at pHpzc 7.5 and 8. The calculated Qmax value for rare-earth element biosorption was approximately 23 mg/g, and Langmuir isotherm models effectively described metal sorption equilibria. Genomic exploration identified genes related to extracellular polymeric substance formation, providing insights into underlying mechanisms. This study presents the first evidence of efficient La, Eu, Gd, and Sm adsorption by SH31, emphasizing its potential significance in rare-earth element recovery.