Biosorption of rare earth elements by Escherichia coli displaying a cyclizable terbium(III)-binding peptide

Efficient recovery of rare earth elements (REEs) is essential for sustainable technologies. We evaluated a synthetic cyclizable peptide (peptide 2) for bacterial biosorption. Fluorescence resonance energy transfer analysis, utilizing non-linear regression models, revealed that peptide 2 possesses high affinity for middle-range lanthanides, such as Tb³⁺, Gd³⁺, and Dy³⁺. Disulfide-mediated cyclization significantly enhanced binding affinity, yielding a dissociation constant of 2.6 nM for Tb³⁺. To develop a practical biosorbent, we engineered Escherichia coli to display peptide 2 on its outer membrane via the OmpC protein. These recombinant strains exhibited a standardized adsorption capacity of up to 1.11 mg Tb/g dry biomass, representing a statistically significant improvement of up to 33% compared to the native OmpC control. These results highlight the potential of surface-displayed cyclizable peptides for developing efficient, REE-specific biosorbents.