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The Bioleaching aspect of our project utilises the performance of Acidithiobacillus ferroxidans in oxidizing iron and sulphur containing compounds or minerals. Since this microorganism is difficult to grow in large quantities, we designed a strain of E coli which would be able to perform the same function. The synthesized bacteria would produce two oxidizing enzymes which would allow for the recovery and recycling of lithium from electronic waste. This mechanism specifically involves the oxidation of the ferrous iron to ferric iron and this iron produced further oxidizes the metal sulphides and speeds up the mineral dissolution rate to obtain lithium. The main reaction of lithium metal bioleaching may be summarized as follows:

Lithium detection is one of the functionalities of our project since we introduce a more sustainable and safer means of mining lithium. This is done by using bacteria to synthesize a sensor which is able to detect the presence of lithium in the ground by turning red. The colour change would help inform us of the specific geographic areas where lithium is likely to be found, avoiding the problem of mining in areas where there is no lithium present, saving money and resources. This would potentially reduce the negative impacts of mining on the environment and community as well.

Bioleaching Plasmid (6186 bp)

The parts comprising the bioleaching plasmid included the plasmid backbone itself (BBa_J428326) and two main other enzyme parts.

  • Tetrathionate Hydrolase:

    The Tetrathionate Hydrolase, an enzyme which catalyses tetrathionate hydrolysis, plays a distinctive role in the acidophilic iron and sulphur oxidizing bacterium A. ferrooxidans. It is responsible for the dissimilatory of sulphur oxidation to generate sulphate, elemental sulphur, thiosulfate. This part successfully combined tetrathionate Hydrolase protein with a constitutive promoter, a ribosome binding site (BBa_J61100) and a terminator (BBa_B0010).

  • High potential iron Sulphur protein (HiPiP) and pH Resistance gene:

    The HiPiP, as its name suggests, has a high redox potential hence is effective in catalysing the oxidation reaction which takes place. With the lithium biomining process involving oxidation reactions with sulphide minerals, this part plays an crucial role in enhancing the E.coli bacteria lithium recycling activity. During the lithium bioleaching process, it is normal for low pH levels to arise due to the increased concentration of hydrogen ions thus the need for the pH resistance gene. This ensures the growth and metabolism of our strain of bacteria in the bioleaching environment. Synthesizing this complete part involved the use of two promoters, two ribosome binding sites (BBa_J61100) and three terminators (BBa_B0010), as well as the HiPiP and the pH resistance gene.