Construction of a cell surface engineered yeast aims to selectively recover molybdenum, a rare metal

The depletion of rare metals is an issue of major concern since rare metals are limited in the abundance but essential for high technology industry. However, the present rare metal recovery technology by chemical methods has high environmental impact, poor selectivity, and is too expensive to be practical. To resolve these problems, this study aimed to create a rare metal recovery system using yeast, and molybdenum was selected as the first target. A molybdenum binding protein, ModE, which was derived from Escherichia coli was selected. A fusion gene was generated by linking partial modE with a secretion signal and a domain of α-agglutinin to display the ModE on the surface of yeast cells. The expression of fusion protein on the cell surface was detected by immunofluorescence labeling. As for the recovery experiment, the engineered yeast cells were incubated in 10 mM of sodium molybdate solution for 2 h, and the recovery of molybdenum ion was measured by ICP-AES. The results of fluorescence micrographs showed that the designed fusion protein was successfully expressed on yeast cell surface. According to the results of ICP-AES, the cell surface engineered yeast adsorbed molybdenum and the cells after 72~84 h incubation gave the best adsorption. Besides, the results suggested that the optimization of each functional domain in the fusion protein was important. The selectivity and the lower limit of recoverable concentration are under investigation, while this study provides a preliminary result of bio-extraction technology using cell surface engineered yeast.