E. pangu: The Pioneer of Mars

Background

Since the onset of industrial era, the environment on earth keeps getting worse day by day because of the burning of fossil fuel and continuous deforestation. Recently, the discovery of Kepler-452b publicly announced by NASA calls public attention to space immigration again. As a matter of fact, the immigration to Mars, the most earthlike planet in solar system, still should be considered as priority.

Before Mars immigration for human beings, it is necessary to send pioneer organism there to assess the feasibility of human immigration. What’s more, special pioneer organism can be also used to change the Martian atmosphere to make it more suitable for other organisms. The first three gaseous components of Martian atmosphere are carbon dioxide (96%), argon (1.93%) and nitrogen (1.89%)[1]. Among these components, CO2 and N2 are ubiquitous on earth. Thus, SCU_iGEM team aim to create a pioneer organism which is able to carry out carbon fixation and nitrogen fixation simultaneously. After inorganic carbon and nitrogen are fixed into organic substances, they could act as nutrients server for other immigrant organisms in the future.

Project overview

In this summer, we are going to design a system which is able to fix inorganic carbon and nitrogen simultaneously. This system consists of 2 types of E.coli: nitrogen fixation E.coli and carbon fixation E.coli. We hope this system will play the role of pioneer organism on Mars immigration. Based on this purpose, we call them E. pangu collectively, which is named after the creator of universe, Pangu in Chinese mythology, as they will reclaim Mars for future immigrated organisms.

Our project contains the following contents:

1.Nitrogen fixation E.pangu

Azotobacters are nitrogen fixation bacteria. They catalyze N2 reduction into ammonia by nitrogenase. The nitrogen fixation genome contains a large number of modules, or clusters. After deleting unnecessary modules[2], we will transform the minimal nitrogen fixation genome from azotobacter Paenibacillus sp. WLY78 into E.coli to construct nitrogen fixation E.pangu.

2.Carbon fixation E.pangu

Many anaerobes carry out carbon fixation by Wood-Ljungdahl pathway. One of the core enzymes in this pathway is acetyl-CoA synthetase/carbon monoxide dehydrogenase (ACS/CODH), a bifunctional enzyme which can reduce CO2 into acetyl-CoA, the central molecule in metabolism. We will transform the gene of ACS/CODH into E.coli to construct our carbon fixation E.pangu.

3.Testing

In this part, we will introduce gene editing technique called CRISPR-Cas9 to knock off the gene of pyruvate dehydrogenase(PDH) complex of carbon fixation E.pangu. Without PDH, the normal pathway of acetyl-CoA producing is cut off. Thus, if our carbon fixation E.pangu was successfully constructed, they can grow normally without PDH.

Reference

[1]Krasnopolsky, V A.; Feldman, P D. Detection of Molecular Hydrogen in the Atmosphere of Mars. Science, 2001, 294:1914-1917.

[2]Wang L, Liu Z, Zhao D, Liu X, et al. A Minimal Nitrogen Fixation Gene Cluster from Paenibacillus sp. WLY78 Enables Expression of Active Nitrogenase in Escherichia coli. PLoS Genet, 2013, 9:e1003865.

[3]Lindahl P A. The Ni-containing carbon monoxide dehydrogenase family: Light at the end of the tunnel. Biochemistry, 2002, 41:2097-2105.