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:
Ensuring a stable energy supply is the central challenge of the 21st century, and this team will highlight the importance of the problem and prepare the next generation of scientists. In additional to the technical goals, this project is envisaged to have broader impacts in four distinct domains:
1. 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.
2. Students will be important stakeholders in the Plug and Play (P&P) team and funds have been included for all American PIs to include summer, undergraduate students in their research. Furthermore, the proposed project offers extraordinary training opportunities to students at all levels. Unique to this project and multidisciplinary team is the range of scientific disciplines and academic institutions involved. In particular P&P includes representatives from the fields of microbial ecology, synthetic biology, protein biochemistry, protein design spectroscopy, electrical engineering and bioinorganic chemistry, and its members work in labs in seven universities in the U.S. (Arizona State, Michigan State, Penn State, Emory) and the U.K. (Glasgow, Southampton, Imperial).
3. The P&P team exemplifies the globalization of science and will serve as a model for collaboration between the NSF and the BBSRC. Recognizing the importance of international collaboration, we have carefully constructed a trans-Atlantic administrative structure to foster close ties and included funds in the budget to support exchange of scientific personnel between laboratories.
4. Dissemination of scientific results will be crucial to this project, both to push the boundaries of photosynthetic research and engage the public in understanding a crucial problem. The geographic disparity of the participants provides a unique opportunity to develop web-based photosynthetic resources to engage the international community.