Design Principals of Photobiological Metabolism

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Cellular metabolism encompasses the fundamental processes by which organisms acquire, store, and release factors required to respond to changing needs and environmental conditions. In photosynthesizing organisms, the basis for cellular metabolism is drawn from the controlled capture and utilization of solar energy, a process which is essential for virtually all terrestrial life. Chemically, the early reactions of photosynthesis involve the absorption of incident solar light and its conversion into low potential electrons that can be used to drive a variety of metabolic processes, including carbon fixation. Regulation of the direction of electron flux towards different metabolic processes is largely controlled through the actions of the electron carrier, ferredoxin. However, the mechanism by which ferredoxin preferentially donates low potential electrons to one metabolic pathway over another is poorly understood. To this end, I propose to examine the plasticity of electron flux from ferredoxin within the cyanobacterium Synechococcus elongatus PCC7942. Specifically, I propose a series of experiments designed to redirect low potential electrons towards cellular hydrogenases, which catalyze the production of hydrogen gas as a readout of accepted electrons. Proposed experiments involve the construction of cyanobacterial strains with inducible downregulation of metabolic pathways competing for low potential electrons as well as strains with ferredoxin and hydrogenases spatially constrained together by expression of chimeric proteins or synthetic protein scaffolds. These experiments will result in the construction of strains of cyanobacteria capable of producing hydrogen gas directly from sunlight. The results of these experiments will have relevance for the understanding of photosynthetic metabolism. Furthermore, these experiments will have broad implications for the engineering of photosynthesis-driven pathways for the production of biomedical compounds and sustainable, clean biofuels.