S17: Cyanobacteria as solar-powered biocatalysts for biofuel production

Photosynthetic microbes are effective in producing organic compounds, some of which can be used as biofuels, starting from CO₂ and water and using sunlight as the energy source.  Many algal biofuel approaches require cell harvesting, processing and extraction, which are laborious and expensive.  Instead, our approach focuses on excretion of the biofuel product from the photosynthetic organism, so that just the product needs to be harvested.  In this way, the photosynthetic organism serves as a biocatalyst, and biomass production is no longer a goal.  This not only saves processing and extraction costs, but also minimizes continued inputs of nutrients.  As in most cases organisms do not excrete valuable organic compounds, a genetically tractable system is required.  To produce and excrete the free fatty acid laurate, we equipped the cyanobacterium Synechocystis sp. PCC 6803 with a suitable thioesterase and deleted an enzyme used for the reutilization of free fatty acids.  The resulting organism efficiently produces and excretes laurate, which subsequently is harvested.  The harvested laurate is then converted to n-undecane by decarboxylation via the Centia^TM process, and can be isomerized further to jet fuel, etc.  Upon introduction and/or deletion of the appropriate genes, this cyanobacterial system is suitable for efficient production of a number of biofuels and petroleum substitutes, without requiring cell harvesting and extensive processing.  Funded by ARPA-E.