Partnership

We first decided to meet with the Evry iGEM team to discuss each of our projects, and we quickly discovered that both our teams were working on projects based on a Microbial Fuel Cell (MFC). iGEM Evry is currently working on the diagnosis of kidney cancer by sensing lnRNA (long non-coding RNA), and their goal is to have an electric reporter system that can detect lnRNA associated with this cancer. On the other hand, our MFC has to produce the maximum current possible from a sugar-based waste: brewers’ spent grain. It is important to note that the Evry iGEM team does not use Shewanella oneidensis like we do, but our two teams do use the same cytochrome c-based proteins, mtrC.

Together, we discussed what materials we could use to maximize the electric current of our original design. We first decided to use carbon fibers as anode and cathode attached to iron electric wires, which were shown to have one of the best electric conduction without being a noble metal. As we were currently using carbon fiber felt, the iGEM Evry team told us about a scientific article that showed that using graphite fiber brush[1] increases power production.In addition to the materials change, we also wanted to improve the medium to increase the electron transfer to the anode.

Firstly, we talked about MFC components: we both used the same software, SolidWorks, and a 3D printer in order to design and print our MFC, so our devices did not have major differences in their components.

However, our systems were different: iGEM Evry and us had both chosen carbon fibers for our anode and cathode, but our electric wires were composed of iron and the Evry team used titanium. Both elements have a great electric conductivity but titanium is slightly better.
Our choices were in accordance to the goal we sought:

• Either having a great sensitivity with detecting long non coding RNA;
• Making a pollution-less microbial battery that uses iron over titanium (2.2 tCO2/t versus 30 tCO2/t) [2].
  
  

During our discussions, iGEM Evry informed us on the issues they were facing with their MFC. In order to be able to help them, we gave them some of our Shewanella oneidensis strain so that we would have similar conditions for both our MFCs, which would make it easier to figure out the problem. Following this, we found out what could be one of the issues with Evry's device.

Indeed, we have different anodes and cathodes: Evry's team use brush-shaped carbon fibers while we use curled up carbon fiber felt. At first, we believed that since their brush electrodes occupied almost fifty percent of the chamber space and that we were using electron shuttle mediators (as phenazine and canthaxanthin), we would get a better biofilm formation thanks to the large surface area. A biofilm is a gathering of bacteria bound to each other, it increases the electric output and is known as one of the best ways to increase it using an electroactive micro-organism as Shewanella oneidensis [3].

However, this hypothesis ended up being false, and despite the brush-shaped carbon fibers having increased power production, it is not optimal for the formation of bacterial biofilm. But the iGEM IONIS results showed that the curled up carbon fiber felt was a much better option for the formation of the biofilm, which iGEM Evry was able to incorporate for their next experiments.

Both our teams made their first measurements in aerobic conditions, however the IONIS team already knew that anaerobic conditions could significantly improve the biofilm formation and thus, the electric current. Indeed, when Shewanella oneidensis is in anaerobic conditions, genes related to external electrons transfer as the Mtr nano conduct genes are overexpressed compared to those same genes in aerobic conditions. Therefore, iGEM Evry was able to procure some anaerobic atmosphere generation bags that they shared with us. Sadly, we did not have the time to perform the results in time to publish them here.

Moreover, we wanted to transform Shewanella oneidensis in order to overexpress mtrC. However, since we did not have access to an electroporator but iGEM Evry did, they lent us access to it to be able to transform it.

Finally, electron shuttle mediators make the electron transfer from the media to the anode more efficient. Evry's team helped us by giving us some Escherichia coli able to produce the phenazine-1-carboxylic acid, an electron shuttle mediator that was shown to increase by three folds the electric current compared to the riboflavin that we intended to use [4]. However, when our team tried to incorporate this E. coli strain in our MFC prototype, it did not show an increased electrical current. We believe the co-culture of E.coli and Shewanella oneidensis is not beneficial to Shewanella oneidensis, who was probably over-grew by E. coli, thus we got poor results. In our next prototype attempts, we plan on not doing this co-culture, but rather collecting the phenazine-1-carboxylic acid from the E. coli culture to put in the anode compartment with Shewanella oneidensis.

As well as our partnership with iGEM Evry, we also discussed a possible partnership with iGEM UMA, who was working on a project to create starch by degrading the cellulose in biomass. Since our project involves degrading starch, we thought it would be a great opportunity to test both our projects if we both succeeded. Indeed, we wanted them to send us some of the starch that they produced to see if the StarchLight device would be able to degrade it and produce electricity from it.