Engineered phages for selective adsorption of rare earth elements

Biomaterial extraction of rare earth elements (REEs) offers an environmentally friendly and efficient alternative to chemical solvent methods. M13 Phages showing less non-specific REE binding without glycosylated polysaccharides have multiple copies of p8 fusions to display peptides with selective binding for the desired REEs. In this study, we developed two diverse phage display libraries: one displaying 12-mer peptides and another displaying 17-mer circular peptides, each with over 1 × 10⁷ unique peptides. Six fluorescent protein-peptide fusions, CFP-peptide-YFP, were prepared for measuring K_d. Their REE affinity, ranging from 2 to 30 micromolar (µM), were generally weak, but a novel peptide-phage, H11G-p8, a derivative of H11-p8, showed a better affinity toward Eu than others. Recombinant phages displaying H11G and E1 were also assessed for their K_i (phage inhibition) values, ranging 10^-11 to 10^-12 molar (M) resulting from the combination of specific binding to the REE and non-specific binding from the phage backbone. Both phages were further evaluated for direct REE binding as free phages in solution and as immobilized phages bound to resin. Both phages showed preferential binding toward Tb, with H11G-p8 consistently exhibiting higher specific Tb binding, indicating its greater potential for separating Tb from other REEs.