Team:Exeter/Bioreactor
Below, you will find a timeline of design steps that were taken in order to reach our final bioreactor.
Pre-Concept: Deciding On this Project
We wanted to improve upon the bioreactor designed by previous iGEM team, Leiden 2016, so this was where our bioreactor started. It was very simple with mobilised bacteria being mixed with perchlorate in a single chamber.
Specialists in DPRB, John D. Coates and Ouwei Wang had drawn up loose designs for bioreactors using their research. From them we got the idea of using a cathode system to aid perchlorate reduction. After contacting them, we also gained insight into the different parts we needed to insert into our chassis, and the existing parts of E. coli that could be harnessed.
Clive Butler helped us to understand the needs and properties of bacteria that reduce compounds. From him we realised that we would have to supply haemin, molybdenum, and iron sulphate to our E. coli as the enzymes that reduce perchlorate are metalloenzymes.
Existing research into bioreactors indicated that there is a need for a smaller, more efficient bioreactor in comparison to the large fluid and solid bed bioreactors currently out there reducing perchlorate on Earth.
Stakeholders:
John D. Coates
Clive Butler
Concept: A Martian Bioreactor
Dr. Ceri Lewis, an ecotoxicologist, informed us that perchlorate in water sources is not a prominent environmental issue. More information about the spread and severity of perchlorate needs to be known before it can be determined whether this is a sufficiently useful project. It was suggested that there may not be enough demand for a novel bioreactor that bioremediates perchlorate on Earth.
We contacted local water companies, such as South West Water, asking for their opinions on perchlorate contamination and for assays of our local water. They informed us that perchlorate is not a pollutant they are concerned about, and that they do not test for perchlorate in their water.
We also contacted iGEM teams in areas where perchlorate contamination seemed to be problem. Many of the teams had never heard of perchlorate and were unaware it was a problem, though some agreed to collaborate on an assay regardless. This indicated that it is not a major problem, even to those with higher than normal levels. The teams we contacted included those in California and Texas, where perchlorate contamination is most prevalent.
Dr. Mike Allen of Plymouth Marine Laboratory, a biochemist with experience in bioreactor design, advised us that if there was a real effort to remediate perchlorate contamination, it would occur on site and not at water sources. This is due to the soluble nature of perchlorate, meaning it would spread through water sources very quickly. In order to bioremediate it, you would have to run the entire water source through the bioreactor, which is infeasible.
Stakeholders:
Dr. Ceris Lewis
South West Water
US iGEM teams
Dr. Mike Allen
Design 3
After reading Biotechnological Applications of Microbial (Per)chlorate Reduction(Wang & Coates, 2017) we considered the idea of growing E. coli on a cathode in order to provide it with more electrons and speed up the reaction by up to 12%. The paper proposed a bioreactor in which DPRB (disparate perchlorate reducing bacteria) grew on a cathode, supplying ions that seemed to be a limiting factor in the reaction. Hydrogens would pass from the anode to the cathode through a cation selective membrane, aiding the reaction in the diagram (above). This would speed up the first half of the process, converting perchlorate to chlorite, as this is the slower half (as found in the modelling part of the project). We would simply replace the DPRB with modified E. coli.
Design 4
A meeting with Dr Mike Allen from the Plymouth Marine Laboratory introduced us to the concept of Swirl Flow Bioreactors (SFB), which would allow us to mix the perchlorate with the E. coli as well as separating the oxygen, all in one chamber. We took the design of a typical swirl flow and adapted it to fit our needs of having immobilized E. coli and a cathode.
Stakeholders:
Mike Allen: suggested we remove the cathode and focus our efforts entirely on a Martian Bioreactor since he didn't see any place for an Earth based bioreactor within current water purification systems. We decided to focus our project on the Martian aspect, as it had much more potential.
Design 5
In a second meeting with Dr Mike Allen, he also told us valuable information about how our bioreactor would be received within global markets. He informed us of his experience with selling and developing his own bioreactor, and from that, he advised that we focus more on the Mars travel side of the the bioreactor as there wasn’t much room in the market for a bioreactor on Earth.
During this meeting, we decided to remove the cathode from our design as it would provide the opportunity for unexpected chemistry, as well as sparks which would react badly with the oxygen we are producing. This allowed our bioreactor design to simplify significantly and we started making quick progress.
Design 6
Our first SFB without cathodes involved four chambers, one to mix the regolith with water to extract the perchlorate, and three to consecutively reduce the perchlorate into oxygen until none is left. The vortex created in the SFB would sort the contents according to density, forcing the oxygen into the centre of the tube. A manifold at the end of the tunnel containing a small central tube would carry the oxygen out of the bioreactor while everything else would be carried into the next chamber via a larger tube surrounding the oxygen outlet.
Design 7
With a solid base, we began to tweak the design based on the needs of stakeholders *add specific stakeholders*.
- 3D printable to be made on Mars, and anything that couldn’t had to be light and easy to carry on a rocket.
- Low power consumption in order not to drain the resources of the rest of the biodome.
- Shielded from ionising radiation which would affect the E. coli. This shielding also needs to be light enough to take to Mars.
- There must be a way to kill the bacteria in the bioreactor in the case of unwanted mutations or other unforeseen events.
Design 8
Our first remodel of the SFB involved cutting down the number of chambers requiring propellers in order to reduce the power consumption and resources needed.
- Françoise Bichai, Benoit Barbeau (2006) Assessing the Disinfecting power of Chlorite in Drinking Water (DOI: 10.2166/wqrj.2006.041)
- Ouwei Wang, John D. Coates (2017) Biotechnological Applications of Microbial (Per)chlorate Reduction (DOI: 10.3390/microorganisms5040076)