The Looming Energy Crisis
The global population currently faces a looming energy crisis(1,2). Fossil fuels - the traditional sources of energy used to facilitate human civilisation - are dwindling in supply(1). Therefore, alternative energy sources must be discovered and developed in order to achieve future energy security.
Renewable energy technologies which indirectly harness the power of the sun - such as wind and wave power - are currently utilised across the world in varying degrees(2,3). It is also increasingly popular to directly harness solar power by converting light energy to electrical energy in solar cells(3). However, there are issues associated with the implementation of this technology such as the energy-expensive nature of solar cell and battery construction and maintenance.
Photosynthesis - Nature’s Answer to the Problem
It's well known that photosynthesis is nature's own way of converting light energy from the sun into chemical energy in the form of glucose. The goal of Macquarie University's 2015 iGEM team - the Solar Synthesisers - is to utilise the solar-harnessing powers of chlorophyll and photosystem II in order to produce an environmentally friendly and renewable source of chemical energy, namely hydrogen gas. When combusted hydrogen gas produces only water and energy - this is highly desirable from an environmental perspective(4).
The Solar Synthesisers’ Project
To achieve this goal we're building on the work of last year's Macquarie University iGEM team by transforming E. coli with the genes required to complete the chlorophyll biosynthesis pathway and create photosystem II in this bacterial species. These systems will allow for the use of solar energy to split water into positively-charged hydrogen ions, electrons, and oxygen. Our next goal is then to combine the hydrogen ions and electrons produced in this hydrolytic process in a hydrogenase enzyme complex in order to produce hydrogen gas on an industrial scale. Hence in order to produce a renewable and environmentally-friendly source of energy we present the Solar Synthesisers’ 3 step plan: Capture, Transfer and Synthesise!
In order to capture light energy from the sun we aim to use chlorophyll pigment to capture photons. We aim to transform and express within E. coli the 13 genes required to complete the chlorophyll synthesis pathway in this species.
In photosystem II the energy captured by the chlorophylls is used to split water into protons, electrons, and molecular oxygen.
The next step is the combination of two protons and two electrons in a hydrogenase enzyme complex to synthesise hydrogen gas. The commercially-viable production of industrial quantities of hydrogen gas will represent the successful completion of our project.
What is new from last year?
First, we are all new to iGEM!! The full team was only assembled at the end of July 2015, as a capstone class for our Biomolecular sciences major. We completed the genes within the Chlorophyll biosynthesis pathway. We started, and constructed 14 out of the 17 Photosystem-II genes into Biobricks (Results). We modeled the conversion of ALA to PPIX in E. coli, and the production of hydrogen gas using PSII.
Experimental Organism - Why E. coli?
Rather than engineering a naturally-photosynthetic organism and individually targeting genes in a pathway, we chose E. coli as our experimental host so we could engineer an entire novel metabolic pathway of our own design.
Using E. coli as our host allowed us to incorporate the somewhat large and complex chlorophyll-a biosynthesis pathway, comprising 13 genes, as well as all 17 genes comprising PSII. Incorporation of both pathways in the robust and fast-growing E. coli host provides us with a valuable tool with ‘plug-and-play’ capabilities that allow for further future downstream potentials such as re-engineering the pathway to produce other members of the chlorophyll family.
Summary of achievements
- Successful completion of the chlorophyll-a synthesis pathway - all 13 genes required for chlorophyll-a synthesis in E. coli successfully placed into BioBricks
- Functional characterisation of the ChlM (BBa_K1640018) enzyme. Functionality was demonstrated in converting Magnesium-Protoporphyrin IX (Mg-PPIX) to Magnesium-Protoporphyrin IX-Monomethyl Ester (Mg-PPIX-ME). The presence of ChlM further confirmed by running of extracted protein on an SDS-PAGE gel
- Improved the characterization of Gun4 (BBa_K1080003) by showing PPIX binding with an alternate, simpler method and documented it as a contribution under the experience page
- Successfully constructed BioBricks containing 14 of the 17 genes required for biosynthesis of Photosystem II
- Modelling of pathway from 5-aminolevulinic acid to PPIX. This determined what concentration of 5-aminolevulinic acid (5-ALA) resulted in optimum yield of Protoporphyrin IX (PPIX).
- Armaroli, N. & Balzani, V. (2011). The hydrogen issue. ChemSusChem, 4, 21–36.
- Kessel, D.G. (2000). Global warming: facts, assessment, countermeasures. Journal of Petroleum Science and Engineering, 26, 157–168.
- Ellabban, O., Abu-Rub, H. & Blaabjerg, F. (2014). Renewable energy resources: current status, future prospects and their enabling technology. Renewable and Sustainable Energy Reviews, 39, 748–764. doi:10.1016/j.rser.2014.07.113.
- Altork, L.N. & Busby, J. R. (2010). Hydrogen fuel cells: part of the solution. Technology and Engineering Teacher, 70(2), 22-27.