Characterization of Phage Display Derived Phage Clones and Peptides for the Recovery of Valuable Metal Ions from Low Concentrated Water Streams

The long-term safeguarding of material resources is one of the current major economic challenges facing all industrialized nations. In particular, industrially relevant chemical elements, which are required for increasingly complex high technologies, are subject to a high supply risk [1]. For the Member States of the European Union, the Commission already compiled a list of supply-critical materials and an action plan for the implementation of a circular economy several years ago [2]. Low-resource countries such as Germany must focus more and more on the development of secondary raw material sources, effective recycling and new, environmentally friendly extraction methods. Biomolecules with metal-binding properties, especially short peptides, are particularly interesting in this respect, as they bind with high affinity and selectively, even at low concentrations [3]. We have used the commercially available bacteriophage libraries Ph.D.C7C and Ph.D.12 (New England Biolabs, Inc.) to isolate and identify specific binding peptides for several metal ions with different experimental set-ups. Here, we show how the specifically binding phage clones and isolated peptide motifs for nickel, cobalt, and gallium from Phage Surface Display (PSD) were characterized in terms of binding strength and complexation stoichiometry. For example, to specify the binding behavior, adsorption isotherms of two specifically binding phage clones - with the peptide motif CNAKHHPRC for nickel and CTQMLGQLC for cobalt - were determined on metal-loaded NTA agarose beads and compared with wild-type phage. Using different mathematical models, remarkable differences in the binding behavior of these three phage clones were found [4]. Thus, it was successfully demonstrated that the specific binding of these phage clones to chemically similar elements, such as cobalt and nickel can be verified by kinetic data. To corroborate these results, isothermal titration calorimetry studies were performed on pure synthetic peptides. The thermodynamic data also showed different binding properties for both ions. The applicability of this methodological approach was demonstrated in binding experiments with wastewater from the semiconductor industry. Selectively gallium-binding peptides have been shown to retain their binding ability after immobilization on polystyrene beads and are suitable for selective purification of complexly composed waters [5]. Our studies conducted so far indicate that PSD is generally a very suitable tool for the identification of specific binding peptides for metals in ionic form. Therefore, PSD can be considered as a platform to develop a green technology for the recovery of strategically important metals.