Improving photosynthesis for biofuel production

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Oxygenic photosynthesis is proposed for fuel production on a global scale. A high solar energy conversion rate is needed to make the process feasible. This requirement is linked to the photosynthetic efficiency, i.e., the conversion efficiency of solar energy to organic material.The cyanobacteria are desirable biofuel feedstocks due to their growth on non-agricultural and marginal lands and ability to thrive in brackish and marine waters. However, although their theoretical maximum efficiency of energy conversion is estimated as 8-10%, the best-sustained efficiencies reported are 1-2%.We will investigate cyanobacterial light-harvesting to enhance photosynthetic efficiency. We will explore how carbon dioxide couples to solar energy, as balancing source/sink energies is a strategy for improving photosynthetic efficiency.We have developed technology for identifying CO2-binding proteins (Nature Communications (2018) 9:3092 DOI: 10.1038/s41467-018-05475-z). This technology can identify functional proteins (Science Advances (2021) 7:eabi5507).We have identified a CO2-binding protein in the light-harvesting complex (Nature Communcations (2022) DOI: 10.1038/s41467-022-32925-6). We will investigate the impact of CO2-binding on light-harvesting. We propose manipulating this process to alter source/sink energies and improve photosynthetic efficiency.Year 1. Chemical proteomics and 13C-NMR to demonstrate protein CO2-binding. Quantum yield measurements and ultrafast femtosecond spectroscopy to investigate the influence of CO2 on light-harvesting. Year 2. Generate mutant cyanobacterial strains using CRISPR:Cpf1 mutagenesis. Use steady-state and time-resolved fluorescence spectroscopy to investigate the impact of CO2 on light-harvesting in native phycobilisomes and whole organisms. Year 3-4. Investigate bio-ethanol yield in producing strains in which light-harvesting has been engineered with the mutations identified in Objective 2.