Description

Introducing CalcifEXE

The Exeter 2020 iGEM team would proudly like to introduce you to our project CalcifEXE! This summer, we 10 undergraduate students have come together to design a novel method of calcium carbonate precipitation that aims to be a greener alternative to traditional methods.

Our project is also exploring the idea of applying our engineered bacteria into a 3D bioprinter that is able to construct calcium carbonate into specific crystal morphologies and specific structures. We hope that by incorporating our idea into a 3D printer our project will open up new possibilities in producing custom products for industry in a carbon-mitigated way.

One possible application that we see potential with is the production of custom coral backbones that can be used to help regrow and repair damaged reefs. We look forward to showing you everything we have done over summer while under such challenging circumstances!

What was our Inspiration?

Early on in our initial brainstorming sessions it was clear that the environment was a shared passion and concern amongst our team, resulting in numerous ideas for an environmentally focused project. We all agreed that our project needed to have a real-world impact and to have a positive effect on the environment.

One of the leading concerns globally right now is climate change and the negative effects of global warming on our planet. A gas that contributes to this is CO₂ where huge volumes are released by the manufacturing industry as well as in many other anthropogenic activities. One source of CO₂ emissions is in the production of precipitated calcium carbonate that requires the thermal decomposition of calcium carbonate found in limestone in order to be manufactured. This process releases vast amounts of carbon dioxide as well as many other pollutants due to the fuel required for thermal decomposition. It is estimated that the cement industry products 2.8 Bn tonnes of cement every year which equates to around 7% of the global anthropogenic carbon dioxide emissions [3]. Therefore we set out to find a more carbon-friendly way of producing precipitated calcium carbonate that would also allow for production of a variety specific products.

How did we Choose our Project?

Early on in our iGEM journey we decided on 3 ideas that we believed had potential to develop into successful iGEM projects. Desulphurisation of thiophenes from crude oil, Bio-concrete and plastic degradation.

Having presented these ideas to our supervisors and discussed them with some industry experts who were able to inform us on potential issues, we decided to focus on a particular avenue of Bio-concrete namely the production of calcium carbonate via bacterial precipitation.

What is CalcifEXE?

We aim to engineer the bacteria B. subtilis to increase its capacity and ability to precipitate calcium carbonate. This will be done through a variety of genetic engineering approaches.

Firstly, we will be introducing an efficient carbonic anhydrase enzyme which will be responsible for removing CO₂ from the air and converting it into bicarbonate ions. Secondly, we will try to increase the efficiency of the ureolysis pathway already present in the bacteria via incorporation of specific urease enzymes and identifying applicable accessory proteins via genetic screening. Finally, we will experiment with certain coral proteins known as CARPs responsible for calcium carbonate precipitation in certain coral species.

We hope that our project will be able to be applied to a variety of applications. As a proof of concept our main aim will be producing calcium carbonate coral scaffolds that will replace the current concrete/metal structures currently employed to help regrow coral in severely affected areas.

Urease Pathway — Figure 1 - Schematic Diagram showing hydrolysis of urea and subsequent reactions [1]

What are our Goals?

References

[1] Seifan, M.; Berenjian, A. Microbially induced calcium carbonate precipitation: A widespread phenomenon in the biological world. Appl. Microbiol. Biotechnol. 2019, 103, 4693–4708.

[2] Bilal.bhatti96 https://upload.wikimedia.org/wikipedia/commons/4/4e/Mechanism_for_Carbonic_Anhydrase.jpg

[3] Lewis McDonald, Fredrik P. Glasser, Mohammed S. Imbabi. A New, Carbon-Negative Precipitated Calcium Carbonate Admixture (PCC-A) for Low Carbon Portland Cements, Materials 2019, 12, 554,