Abstract: Rare earth elements (REEs) are metals that are indispensable to the function of many advanced systems and materials. The supply chain of REEs is heavily dependent on foreign sources and supply shortages are a major concern to the US government. Biological recovery approaches could be an economically feasible approach to recover REEs from unconventional or secondary sources. The objective of this project was to express a lanthanide-binding tag, with an affinity for adsorption of REEs, on the surface of the biomining bacterium, Acidithiobacillus ferrooxidans. This was to be accomplished using synthetic biology tools. The initial cloning steps were performed in Escherichia coli, since techniques are well established in this strain. Using a peptide display approach, several DNA constructs with the binding tag were designed that were regulated by constitutive or inducible promoters and cloned into plasmids that replicate in E. coli and A. ferrooxidans. All plasmids were observed to be unstable or lethal in E. coli, exhibiting sequence rearrangements or deletion of the designed construct. Conjugation between E. coli and A. ferrooxidans and subsequent REE binding assays were thus not possible due to the absence of a structurally and functionally intact plasmid.