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From 2014.igem.org

Introduction

Carbon dioxide (CO2) is notorious for its major contribution to global warming, where one of the impacts brought to the ecosystem is its excessive solvation into the ocean in carbonate form, threatening marine lifes (Baldgcchi et al., 1996). This year we would like to utilize and recharge these abundantly available CO2 by converting it to methane (CH4), an important carbon source for fuels and bio-degradable plastic production. While there are naturally existing methane-generating microorganisms, the convertion process involves multi-step metabolic reactions, not to mention that the mircoorganisms can only survive in anaerobic environment. Therefore, the difficulty of manipulating this convertion process remains high.

A recent research showed that a mutated form of nitrogenase from Azotobacter vinelandii, a nitrogen-fixing bacteria found in soil, has carbon fixation ability (Seefeldt et al., 2013). Yang et al. demonstrated that by introducing 70Ala and 195Gln mutations on nitrogenase alpha subunit, the nitrogenase enzyme complex reduced CO2 and CO32- to CH4 instead of converting N2 to NH3 (Yang et al., 2012). This system provided an one-step reaction to convert CO2 into CH4 and other carbon compounds directly. However, since a large electron flux, and thus energy, was wasted in producing molecular hydrogen (H2) from protons during the reaction, we utilized a soluble hydrogenase complex from Aquifex aeolicus to recycle H2 to protons. To further enhance the efficiency of carbon fixation process, we physically linked both nitrogenase and hydrogenase complexes with SH3 and PDZ ligand-domain pairs to accelerate the H2 recycling.