Why we care about cadmium and sulfate in the environment:

Both cadmium and sulfate compounds can be found in wastewater and is produced from processes such as electroplating. If these contaminants are not removed from the environment, they can have a detrimental impact upon living organisms. For example, if cadmium is consumed by mammals over a long period of time, it can cause health problems such as Itai-Itai disease (cadmium poisoning). This year, our project at iGEM York is focusing on increasing the uptake of cadmium and sulfate in our chosen chassis E. coli. The project has two main, interlinked approaches:

• Firstly, the increased uptake of sulfur using an exogenous sulfate transporter from Bacillus.

• Secondly the increased uptake and chelation of cadmium ions through the use of metal-binding proteins, to produce a potentially recoverable metal product.

How are these two processes intertwined?

We are tweaking the cysteine biosynthesis pathway, allowing the over-expression of cysteine and the utilisation of the sulfate that accumulates inside our cell. In addition, we are tweaking another system, the production of cysteine-rich phytochelatins. We are over-producing these metal-binding proteins, and thus creating a sink for the cysteine that is produced by our cell. These metal-binding proteins are also responsible for chelating the cadmium that our cell takes up from the environment.

How is our system regulated?

We have designed our system to be regulated by the concentration of cadmium in the environment. If the concentration of cadmium surpasses the sensitivity threshold of pYoda (cadmium-inducible promoter)then it will activate our system and as a result, our genes will be expressed. Our system prevents the overproduction of cysteine when cadmium is at low concentrations.

Structure of L-Cysteine

Synthesis of L-Cysteine