SusChEM: Biological Auto-Enhancement of CO2 Absorption for Improved Cyanobacterial Growth and Biofuel Production

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Phototrophic microorganisms, which use sunlight to make chemicals for their nutrition, possess potential as "microbial chemical factories" to make sustainable fuels and chemicals directly from atmospheric CO2, using sunlight and water for energy. One technical challenge to this approach is poor CO2 absorption into the aqueous solution containing the microbes. In other industrial processes that convert CO2, use of alkanolamine solvents such as monoethanolamine (MEA), can be used to enhance aqueous CO2 solubility and, in turn, the rate and efficiency of its absorption from gas streams. This project seeks to engineer a model cyanobacterium organism to produce MEA directly via photosynthesis. In the presence of produced MEA, the rate and efficiency of CO2 absorption into the organism's culture medium will be significantly enhanced and, as a result, so too will be rates of cell growth and biofuel production. In addition, a multi-faceted approach to research, education, and outreach will also be included. This project will serve as the basis for several high school and undergraduate student research projects involving the Fulton Undergraduate Research Initiative (FURI), School of Life Sciences Undergraduate Research (SOLUR), and the SCience and ENgineering Experience (SCENE) programs to recruit women and under-represented minority students. A novel metabolic pathway will be engineered to enable MEA biosynthesis from endogenous precursors in Synechocystis sp. PCC 6803. This will be achieved by deregulating a native precursor biosynthesis pathway, followed by the introduction and optimized expression of the heterologous pathway steps. Within the aqueous culture, CO2 will react with produced MEA and then, through a series of subsequent reactions, will ultimately be rendered as bicarbonate. Cellular assimilation of bicarbonate will promote further regeneration of produced MEA, thereby returning it to react again with additional CO2 molecules. To facilitate the biological regeneration of MEA, the project will include strategies to enhance bicarbonate uptake. In the end, enhanced CO2 absorption will support higher growth rates of the microbes, increased growth will support higher rates of MEA production, greater MEA availability will support further improved CO2 absorption, ultimately resulting in an auto-catalytic effect. These strategies will be investigated in both wild-type Synechocystis as well as a previously-engineered laurate-producing strain, thereby allowing the effects of MEA biosynthesis on the production of this important fatty acid biofuel precursor to be explored.