Solar energy is a sustainable resource exceeding predicted human energy demands by >3 orders of magnitude. If this diffuse solar energy can be concentrated and stored efficiently, then it has the capacity to provide for future human energy needs. The process of oxidative photosynthesis, namely the reduction of CO2 utilizing light and water by photoautotrophs, stores solar energy in reduced carbon compounds, which are useful fuels for society. Although oxidative photosynthesis evolved some 3.5 billion years ago, it remains inefficient at converting solar energy into chemical energy and, ultimately, biomass. Commercial photovoltaics in concert with electrolyzers split water to produce hydrogen at an efficiency of approximately 10%. Photosynthetic yields for plants in optimal conditions typically do not exceed 1%, and higher-yielding microalgae species are estimated to have 3% efficiency. Under most conditions, the biological transformation of light to stored chemical energy is not limited by light but by the rate of carbon reduction. The goal of this project is to engineer pathways for diverting photosynthetic energy from linear electron flow (LEF) to alternative sinks, thereby providing alternate routes for "excess" photosynthetic capacity when carbon fixation is saturated. Our strategy is to engineer an intercellular, plug-and-play platform (PNP) that allows us to move electrons and/or reduced chemicals from modified photosynthetic source cells to independently engineered fuel-production modules that bypass the inherently inefficient
carbon-fixing catalyst RuBisCO. The realization of this goal will require radical manipulation of the fundamental biology of photosynthesis and development of novel synthetic biological, chemical, and analytical techniques.

Technical Abstract:
Solar energy is a sustainable resource exceeding human energy demands by >3 orders of magnitude. If this diffuse energy can be concentrated and stored, it has the capacity to provide for human energy needs. The biological transformation of light to chemical energy (photosynthesis) is limited by the rate of carbon reduction. The goal of this project is to engineer pathways for diverting energy from carbon reduction to alternative sinks.
Our strategy is to engineer an intercellular, plug and play platform that allows electrons and/or reduced chemicals to move from photosynthetic cells to engineered fuel production modules, bypassing the inefficient carbon-fixing catalyst RuBisCO. This will be achieved by increasing flux through natural electron dissipation pathways, creating electrical connections between cell types, and employing a soluble redox shuttle to transfer reducing equivalents between cells. This international and interdisciplinary project is building bridges between the US and UK scientific communities in critical areas of synthetic biology, photosynthesis, electro-chemistry, catalysis, and metabolic regulation.
The scientific goals are organized around 4 specific aims. 1 Characterize components and control flux through the natural photosynthetic pathways in the cyanobacteria Synechocystis. 2 Construct artificial systems to sink reducing equivalents from photosynthesis. 3 Develop artificial means to move reducing equivalents outside the cell. 4 Produce artificial fuel production modules that require only reducing equivalents and CO2.
The project represents a radical approach to surpass natural photosynthesis by engineering a modular division of labor through electrical/chemical connectivity. The aims are devised to generate transformative research for technological applications and enable the discovery of fundamental science. Our goal, therefore, is to establish a platform to open a vast new frontier to develop new modular photosynthetic technologies.

Potential Impact:
The long-term goals beyond the immediate project are to develop a pipeline of synthetic biology knowledge, skills, and personnel to rapidly optimize host organisms for the carbon neutral bioeconomy. This pipeline will support the UK bioprocessing, chemical, and energy industries and communities by acting as a hub of technology and will build the 'human infrastructure' of trained professionals. It is anticipated that the knowledge and technology infrastructure will ultimately accelerate time to market for developed and emerging bioprocessing applications.

Who will benefit from this research?
The synthetic biology / carbon fuel industry, as well as human society as a whole and the environment, will be the major beneficiaries of this research at all levels from multi-nationals to SMEs and spin-out companies. In addition, UK/US HEIs, students and the general public will also be beneficiaries, not to mention the UK/USA-plc as a whole. Also, the successful completion of the scientific goals of this program will transform thinking about photosynthesis by creating independent modules for studying and optimizing the light and dark processes as well as portable biowires to establish functional contacts between distinct cell types. These modules, as well as the platform for testing them as a system, will be freely shared with other researchers i.e. an open source technology approach. The successful completion of the project objective will enable potential adoption of new routes to sustainable materials, allowing industrial and academic users to explore a range of renewable bio-products in a rapid and cost-effective manner.

How will they benefit from this research?
Industry: The synthetic biology / carbon fuel industry will benefit from the new technologies generated in this research since it will provide performance upgrades to photosynthetic devices, as well as establishing a new solar-fuel paradigm that is RuBisCO independent. In particular, the need to bypass biological limitations for carbon capture is required to ensure that photosynthetic fuels can become a commercial reality. These benefits will be of great interest to SMEs and spin-outs that supply synthetic biology components and develop niche applications that will directly utilize and develop some of the technology in other directions, developing niche high-value applications. For instance, the knowledge generated could have third-party applications in new solar-fuel-cell devices that exploit, at a fundamental level, the new opportunities that multi-level devices have. The race to produce a realistic solar-fuel-system is gathering pace and this proposal could ensure that the UK-USA becomes the focal point for this development rather than the far east, Russia, or South Africa.
Education and Training: The interactions between molecular and synthetic biologists, inorganic chemists, and metabolic engineers proposed in this grant will also yield great potential teaching and research benefits for the students and the universities. This is because we estimate >20 undergraduate, >4 ERASMUS, and >12 PhD students will get the chance to take part in research that crosses the interface of this project and it may also be possible to develop a research masters based on this area that will train the next generation of researchers and engineers for solar fuels and photosynthesis.
General Public: The general public will benefit from this research due to the increase in wealth that will be developed and from the public understanding and promotion of science activities and public lectures planned for the UK and US sites.