IGEM:University of Illinois Urbana Champaign/2009/Notebook/Bioware 2010 Gold Bioremediation

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Description/Abstract
The Gold Bioremediation project's goal is to design bacteria capable of binding and removing gold ions while making the bacteria super-resistant to high concentrations of gold.

The physical properties of gold are very similar to physical properties copper, and consequently, gold binds to and inhibits copper-dependent enzymes. Therefore, in order to have cell that are capable of binding to and removing gold ions from water, they must be resistant to high concentrations of gold. To achieve gold-tolerant cells, the efflux pumps GolT and GesABC, which pump gold ions out of the cell, will be overexpressed in the cells when gold is present.

The cells' ability to bind gold ions is conferred by the protein GolB, which binds one gold ion per protein. In our engineered cells, GolB will be constitutively expressed and displayed on the outermembrane. Displaying GolB on the other membrane of the cell, rather than in the cytoplasm, is advantageous for several reasons. One reason is speed; since GolB is on the outside of the cells, gold ions can be collected immediately upon contact, instead of first needing the gold ions to diffuse into the cells. Another reason is toxicity; gold is very similar to copper, so it can be assumed that overexpressing GolB in the cytoplasm will cause GolB to bind some of the free copper within the cell, thus reducing the amount of available copper for copper-dependent enzymes. Finally, placing GolB on the surface of the cells allows for easy purification of gold for future uses and makes the cells reuseable. After the cells have bound gold, they can be gathered and simply washed with a salt solution to elute gold ions from their surface and into solution. Then, the cells can be placed back into the water to collect more gold ions.

The detected of gold will be controlled by GolS, which is a transcription factor that induces transcription upon binding gold ions. In particular, GolS will control the expression of gas vesicles. Once cells have their surfaces saturated with gold ions, the ions will enter into the cell, bind GolS and induce expression of gas vesicles. After the gas vesicles are expressed, the cells will float to the surface of the water, where they can be easily gathered.

Gold is used for a myriad of applications, such as cancer treatment, molecular labeling and making electrical wiring, just to name a few. Because gold is an extremely valuable resource, methods for collecting it are highly desired. There is an abundance of soluble, ionic gold in water sources throughout the world and as much as 15,000 tons of it in the oceans. Therefore, since our system can collect gold when it is present in both minute or high concentrations, and with the fact that our cells would be cheap and reusable, it has great potential as a new method for collecting gold.