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This year, iGEM York are working on a bioremediation project; the decontaminating wastewater. Our aim is to increase sulphate uptake and chelate Cadmium (a toxic heavy metal) through the use of metal-binding proteins called phytochelatins in E.coli. Our project is divided into two main approaches that are interconnected:

• The increase of sulphate uptake (using an exogenous sulphate transporter from Bacillus) and its conversion into cysteine by tweaking the cysteine synthesis pathway.
• The increase of cadmium ion uptake (upregulation of cadmium transporters) and chelation (stabilisation of the metal by metal binding proteins).

The metal binding proteins are the link between the two approaches as they contain sulphur rich cysteine residues which will act as sinks for the cysteine overproduction. The metal binding proteins are divided into two main categories:

1. Phytochelatins (synthesized by a phytochelatin synthetase in a stepwise reaction – so we are working with an exogenous Phytochelatin synthetase gene in E coli)
2. Synthetic phytochelatins (engineered and directly translated from the DNA/RNA sequence without the need of a synthase).

Our system is regulated by the metal concentration in the environment. If the concentration reaches the threshold of our cadmium inducible promoter (pYoda) sensitivity then it will activate the whole system. Thus, our system prevents the overproduction of cysteine when Cadmium is not found at high concentrations.

How would our project be used in practical applications?

In the future, we could imagine our bacteria inside of a semipermeable membrane in a river or water treatment plant with contaminated water flowing through. The high metal concentration would activate the system and our bacteria would start harvesting the pollutants. It could be coupled to a biosensor and then, when a Cadmium concentration threshold is reached the bacteria could change colour, from white to red. This colour change would indicate that it is time for “harvesting”. When this colour change is elicited, the cells could either be lysed by a chemical process or even induced to do it by a kill switch and the metal could then recovered and sold for commercial gain making decontaminating water profitable!

In the future, we wish to investigate chelating other metals that are also found in waste water that have greater monetary value. Vanadium for example, could be chelated in a similar process to our system outlined above and sold on.