Overview

Nitrogen takes up almost 4/5 in earth’s atmosphere. However, it cannot be assimilated as carbon dioxide by plants. Plant productivity has been circumvented in contemporary agriculture by this limitation. In order to break the limitation, chemical nitrogen fertilizers are applied with the invention of ammonia synthesis technology. The chemical reduction process of nitrogen consumes large amounts of energy and the reactive nitrogen released into the environment leads to greenhouse emissions, widespread eutrophication of aquatic ecosystems. (Rogers & Oldroyd, 2014) Moreover, the application nitrogen fertilizer, such as carbamide, ammonium nitrate, ammonium sulfate will also make the soil crust and hard to sow. (Alvarez, 2005) Chemical fertilizers will also lead to low agricultural productivity and malnutrition. (Rogers & Oldroyd, 2014) Biological fixation of nitrogen does not have these disadvantages and it is a promising eco-friendly way to replace the traditional industrial synthetic method.

Azotobacter is also called nitrogen-fixing bacteria, which plays an important role in symbiotic nitrogen fixation. Although some archaea can also fix nitrogen, they only make up a small percentage of biological nitrogen-fixing. Hence, most of the research works focus on azotobacter and the study it can be divided into three sub-areas (Shen & Jing, 2003), which are the study of the factors that affect the efficiency of nitrogen fixing of azotobacter, the study of enlarging azotobacter’s symbiosis range and the study of azotase.

The Promethus program aims at improving the efficiency of nitrogen fixing via the first sub-area. Metals are key elements of all living organisms, including bacteria and plants (Silava & Williams, 1991) and they are an integral part of 30-50% of a typical cell (Waldrom & Robinson, 2009). Metal，such as Fe, Zn, Cu, Ni involves in many important biological process, including the legume-specific stages of symbiotic nitrogen fixation. (Gonzalez-Guerrero et al, 2014) Molybdenum is also an integral part of protein ModA, which is an essential enzyme for azotobacter to fix nitrogen.The ModA protein was localized to the periplasmic space of the cell, and it was released following a gentle osmotic shock. The N-terminal sequence of ModA confirmed that a leader region of 24 amino acids was removed upon export from the cell. ModA gene product is essential for high affinity molybdate uptake by the cell.

A plasmid was transfer into E.coli Promethus to make it express a special fusion protein, one side of which anchors on the out membrane and the other side of which catches molybdate. The engineered E.coli Promethus can bind molybdate and with the help of auxin tendency system design by Imperial College 2013, our Promethus will head for the roots. A suicide system depending on time is also design by us for the reason of bio-safety. E.coli Proethus will deliver Mo directly to the root of plants, so the heavy mental pollution of Mo will almost decrease to Zero according to our experiment results. This will also open a new chapter of biological fertilizer.

References

Gonzalez-Guerrero, M., Matthiadis, A., Saez, A. & Long, T. A. (2014) Fixating on metals: new insights into the role of metal s in nodulation and symbiotic nitrogen fixation. Plant Science, 45(5), 1-6.

Silva, J. J. R. F., & Williams, R. J. P. (2001). The biological chemistry of the elements: the inorganic chemistry of life. Oxford: London.

Rogers, C. & Oldroyd G. E. (2014) Synthetic biology approaches to engineering the nitrogen symbiosis in cereals. Journal of Experimental Botany, 65(8), 1939–1946.

Shen, S. H. & Jing, Y. X. (2003). The review of nitrogen fixation research and prospect in China [中国生物固氮研究现状和展望]. Chinese Science Bulletin, 48(6), 535-540.

Alvarez, R. (2005). A review of nitrogen fertilizer and conservation tillage effects on soil organic carbon storage. Soil Use and Management, 21(1), 38-52.

The Story of E.coli Prometheus

BNU-China