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Technology

These inventors have developed three techniques to remove heavy metal waste including cell surface display of metal binding proteins, cellular uptake to capture metals, and biomineralization. The first technique uses a secreted fusion protein of glutamine synthetase (GS) and metallothioneins (MT). GS has a unique ability to form complex scaffolds in the presence of divalent metals. Metallothioneins are plant-based proteins that have specific metal binding capacities. When these proteins are secreted as a fusion protein along with yeast expressing surface displayed GS, they efficiently bind heavy metals in solution and form dense yeast-metal aggregates that are easily removed from the water. The second metal remediation strategy uses direct metal uptake into the yeast using transmembrane metal transporters. These inventors performed successive rounds of mutagenesis and selection on the yeast metal transporter SMF1 and successfully generated SMF1 transporters that specifically and efficiently uptake cadmium, lead, and strontium. The final bioremediation technique these inventors use is biomineralization of metals. Sulfur is a reactive element that can react with metal ions to form inert metal sulfides. Sulfur has been used in industrial chemical precipitation, however, the volatility of sulfur makes it hazardous to store. Sulfur is a necessary element for life, and biochemical sulfur assimilatory pathways are required to make sulfurous amino acids. These inventors engineered yeast with a strategic block in a sulfur assimilatory pathway that leads to sulfur buildup. These sulfur producing yeast are very efficient at precipitating copper, cadmium, zinc, lead, and mercury, into dense aggregates in the yeast cell membrane. Together, these technologies provide a diverse array of metal remediation strategies.