Difference between revisions of "Team:CHINA CD UESTC/Description"

This summer, CHINA_CD_UESTC team made a high-efficiency enzymatic biofuel cell (EBFC) by constructing magnetotactic E.coli which can produce laccase. In order to achieve success. The four operons, mamAB mamGFDC mamXY mms6, related with magnetosome formation were transferred into E.coli, and we also co-transfered a gene coding a fusion protein which contained laccase and MamW, a magnetosome transmembrane protein as a connection between magnetosome and laccase. So we can fixed laccase on the magnetosome membrane (MM) and utilized the magnetotaxis to gather oxidoreductases on the cathode to improve the efficiency of EBFC.

Along with the development of times and population growth, energy consumption is increasing rapidly. Up to now thermal power is the main source. According to BP Energy Outlook 2035 , from Energy Outlook, we can find that world's fossil fuel reserves decline [1]. And the largest shifts of share give us an insight into the most likely shape of the future energy landscape! (Figure 1)

Figure 1:There have been some rapid shifts in fuel shares in power generation in the past: oil gaining in the 1960s and losing in the 1970s; nuclear picking up in the 1970s/80s and falling in the 2000s; gas rising through the 1990s and 2000s. In the Outlook, the largest shifts are the increase in the renewables share and the decline in the coal share ^[1]

In numerous renewable energies, bioenergy is a kind of clean renewable energy and as a potential excellent substitute for fossil fuel. With the advent and advance of biotechnology, biofuel cell (BFC) that can convert the chemical energy of fuel into electric energy by using enzyme or microbial tissue as a catalyst has been researched and improved.

Previous iGEM teams had done some studies of microbial fuel cell (MFC). iGEM13_Bielefeld-Germany made an Escherichia coli Fuel Cell platform to provide for an efficient electron transfer from the bacteria to the electrode. iGEM14_LZU-China cloned a NO3-sensor sequence and a riboflavin producing genes into Escherichia coli for anode and gene coding chromate (VI) reductase Yief was cloned into E.coli for cathode. iGEM14_SCAU-China boosted up intracellular NAD+(H) level for higher electron transferring rate.

Focusing on EBFC can not noly contribute to promote the development of renewable energies but also enrich the iGEM database.

In our project, we paied attention to laccases which are copper-containing oxidoreductase. It was able to oxidize a broad range of substrates by reducing oxygen to water. In the reduction reaction, the electron from the oxidation is transferred to the other three copper ions. These ions form a trinuclearic cluster, which transfers electrons to the terminal electron acceptor oxygen^[2]. Those excellent electrochemical characteristics of laccase make it an ideal catalyst for biological cathode^[3].

Figure 2: An electrochemical phenol biosensor based on the immobilization of laccase (Lac) on the surface of copper capped magnetic core–shell (Fe3O4–SiO2) nanoparticles (MNPs) ^[4].

We obtained the laccase from BBa_K863005 and learned about that enrichment of laccase was able to improve catalytic efficiency^[2]. But traditional chemical approaches^[4] to fix laccase were complicated, and cost too much, the bioaffinity of laccase was also not up to the expectation. So, we hoped to find a better method!

Biological methods were the better choices to achieve our objective. Magnetotactic bacteria (MTB), a kind of bacteria that can be attracted by magnet, was a superexcellent choice for our EBFC. We noticed that MTB contains a fantastic structure-magntosome, some magnetic nano materials covered by biofilm. The magnetosome was essential to magnetotaxis.

Figure 3: Transmission electron microscopy images of several different MTB showing their distinctive cell and magnetosome crystal compositions and morphologies. Scale bars = 500 nm in bacterial images and 100 nm in magnetosomes images ^[5].

After our discussion, we decided to connect laccases to the magnetosomes membrane to gather them on the cathode surface utilizing magnetosome's ablity of being directed by magnetic field.

Unfortunately, there were two problems for us to solve. First, MTB is anaerobic meaning it is hard to be raised and modify its genes in normal condition. Second, it is complicated for the mechanism of magnetosomes formation. We are aiming to construct an expression system about magnetosome in E.coli to solve those problems. According to a paper in , we confirmed that transfering four related operons can make other bacteria magnetotactic^[6].

Finally, we co-transferred all the vectors we constructed to make E.coli produce magnetosomes carrying laccases. The special magnetosomes would be used into our EBFC to improve efficiency!