Team:HKJS S/Description

Nitrogenase is known to be the only catalyst for the reduction of nitrogen to ammonia presented in several microorganisms which contribute to 70% of biologically fixed nitrogen. It has been confirmed that three types of nitrogenase exist by nature, i.e., Fe only nitrogenase, V nitrogenase and MoFe nitrogenase. Although the mechanism behind nitrogen fixation is yet to be further investigated, it is known that through the ATP requiring, enzymatic, and multi-electron reduction, dinitrogen can be converted into two ammonia compounds in MoFe nitrogenase. The nitrogenase molybdenum-iron protein alpha chain, nifD, has been shown to be the part of nitrogenase to catalyse the vital enzymatic reactions and where the entrance of substrate channel is located.

Many have built based on this fact and using mutagenesis of the amino acid residues of nifD to manipulate the access of substrates. The mutated sites cause substrates to be blocked away from the binding site or trapped in the substrate channel, hence allowing the only specific substrate to undergo the multi-electron reduction or quenched in the intermediate stages. In recent studies, many have managed to induce reduction of other substrates in place of dinitrogen through amino acid substitution in nifD, resulting in different products.

Although many have successfully converted carbon dioxide to methane using a modified nitrogenase, no studies have shown that such reduction can be induced in E. coli as the native host. Base on the fact that E. coli are known to be one of the fastest growing bacteria among all, we propose an efficient carbon dioxide reduction system within E. coli through the expression of the amino acid substituted nitrogen fixation genes in MoFe nitrogenase.