The cyanobacterium Synechocystis sp. PCC 6803 is spontaneously transformable and has a very efficient double-homologous recombination system, making it efficient for targeted metabolic engineering for the production of fuel and chemical feedstock.12, 13 A major advantage of a photosynthetic microorganism as a feedstock producer is that its inputs can be simply CO2, water, and sunlight. If the product can be excreted from the cell, then the photosynthetic microorganism functions as a biocatalyst, and significant growth of cells in the reactor is not required for optimal production. This virtual independence from growth enhances the amount of fixed carbon that can be applied toward the generation of the desired product truly a photosynthetic factory. Excretion of large amounts of organic product from the cyanobacterial cells is not a positive trait in evolution; therefore, metabolic engineering has to be applied to generate the desired products. To maximize success in this project, we will focus on compounds produced by pathways that naturally have a high metabolic flux in cyanobacteria. Synechocystis has an innately high metabolic flux towards fatty acid biosynthesis in order to satisfy photosynthesis-related requirements for internal membranes (thylakoids), which makes this cyanobacterium particularly well suited for production of carboxylic acids. Figure 1 illustrates our successful strategy for producing and excreting laurate. A thioesterase gene from a plant is introduced, and a native fatty acyl-ACP synthetase gene, the product of which allows free fatty acid to be reincorporated into the lipid biosynthesis pathway, is deleted. This direct-production strategy is very efficient in terms of solar-energy conversion efficiency, since little energy needs to be diverted to biomass synthesis. Rates of laurate biosynthesis in our Synechocystis strain currently are up to 30 mg/L/day so far, and the energy in produced laurate can represent 2-3 % of the light energy absorbed by the cells. Laurate is readily excreted by the cells, thus avoiding a significant amount of feedback inhibition.
|Effective start/end date||12/1/12 → 11/30/14|
- DOE: Golden Field Office: $496,906.00
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