Recovery of Rare Metal Ions

Abstract

Metals are essential materials that play an important role in several processes of life. Some metals are necessary as trace nutrients but can be toxic at excessively high levels. Other metals are nonessential and toxic even at trace amounts. Along with the development of the high-tech industry in recent years, the use of metals, such as rare metals having various useful characteristics, has been promoted. Rare metals are also called industrial vitamins and are indispensable for various high-tech products. Therefore, their importance has been increasing in recent years. Cell surface adsorption of metal ions can be used not only for removing toxic metal ions but also for recovering useful and rare metal ions. By displaying the proteins that can bind to rare metal ions on the cell surface, it is possible to construct surface-engineered yeasts that can adsorb rare metal ions such as molybdate or uranyl ions. It is important to possess the ability to selectively recover target metal ions from complex ion mixtures, which can be achieved using protein engineering. For example, the introduction of an amino acid mutation into the molybdate-binding protein (ModE) displayed on the yeast cell surface has allowed for the selective adsorption of tungstate ions. Creation of novel metal-binding proteins/peptides with the ability to selectively sequester target rare metal ions is crucial for further development of the technology required to improve our capability of recovering rare metal ions from the aquatic environment using genetically engineered microorganisms.