Engineered yeast sequesters heavy metals

Plants that can absorb and tolerate high concentrations of metals—so-called hyperaccumulators—offer a promising approach to bioremediation of soil contaminated with heavy metals. But plants aren’t easily engineered, have a long life cycle, and may require growing conditions that are difficult to maintain. To sidestep some of these challenges, Angela M. Belcher, George L. Sun, and Erin E. Reynolds of the Massachusetts Institute of Technology turned to yeast. Because it’s eukaryotic, the yeast Saccharomyces cerevisiae has a metal transport system similar to the one in plants. But because it’s single celled, yeast is easily engineered. The MIT researchers turned yeast cells into hyperaccumulators by making the cells express large quantities of metal transporter proteins, some of which take up metals from the environment and some of which move the metals into vacuoles in the cell (Nat. Commun. 2019, DOI: 10.1038/s41467-019-13093-6). The team designed metal transporters to be selective for various metals. Engineered yeast with the transporters were able to absorb and tolerate metal concentrations 10–100 times as high as the established hyperaccumulation thresholds for chromium, arsenic, and cadmium in plants. By mutating a metal transporter protein, the researchers were also able to engineer yeast that could sequester cadmium and strontium, including radioactive ⁹⁰Sr. Such yeast could be used to clean up industrial metal contamination or to recycle heavy metals from waste streams.