Acetate and alternatives to the photosynthesis economy

 

Agriculture requires photosynthesis to make food. However, the photosynthetic mechanism is slow,  inefficient and requires a lot of resources. A recent paper describes an electro-agriculture technology that combines carbon dioxide electrolysis with biological systems to boost the efficiency of food production. If implemented at scale, such a system could reduce agricultural land use in the United States by nearly 90% and allow food to be grown in urban areas and deserts without the need for light or pesticides. It would also allow more efficient fertilizer use.

“The most readily consumable carbon sources produced via CO2 electrolysis at relatively high efficiencies are ethanol and acetate. Metabolically, ethanol is converted to acetate with alcohol dehydrogenase and acetaldehyde dehydrogenase. Both ethanol and acetate can be used to cultivate common eukaryotic organisms such as yeast or mushroom-producing fungi, which are already consumed as food. Acetate can also serve as the sole carbon and energy source for some species of green algae. Acetate is highly miscible in water and has a one-step metabolic route to acetyl coenzyme A (acetyl-CoA), the biologically active form of acetate that is a substrate in many biochemical reactions. The high miscibility and accessibility to acetyl-CoA makes acetate consumption easy to engineer, allowing acetate to be readily metabolized and used for energy and biomass production. Acetate can also be taken up and metabolized by plants; recently, electrochemically produced acetate has been shown to be able to support the production of crops with a 4x improvement in solar-to-food efficiency over conventional photosynthetic agricultural approaches. The high concentration, efficiency, and purity of electrochemically produced acetate, its short metabolic pathway, relatively high number of donor electrons, and compatibility with many organisms already cultivated for food make acetate the leading CO2 electrolysis product for electro-ag feedstock. 

 

“Most food consumed by humans originates from plants, making it essential for electro-ag systems to produce crop plants effectively. All adult crop plants are photoautotrophic, relying on photosynthesis to build biomass. In an electro-ag system, however, plants must be heterotrophic, consuming acetate to construct biomass. Adult plant metabolism is not optimized for heterotrophic growth on acetate.”

The paper goes on to describe the engineering of plants that grow on acetate electrochemically produced from CO2. The efficient genetic engineering of diverse plant species using CRISPR means that, in principle, many familiar foods could be amenable to the acetate strategy, although I’m not sure how feasible rice production—on which billions of people currently depend—would be.

Is this a practical solution for food production? Even the authors admit that “ . . . given the relatively low market price of staple crops, it will be difficult for electro-ag to be economically deployed at scale in the near future. In the near term, electro-ag is most useful for scenarios where it is otherwise too difficult to produce food via photosynthesis. However, even in these scenarios, electro-ag requires access to relatively large amounts of electricity. If renewables are used, future work is still needed to improve the intermittent operation of the electrolysis system, or energy storage systems must also be deployed.”

Next “green revolution” or biochemical parlor trick? We report, you decide.

https://www.cell.com/action/showPdf?pii=S2542-4351%2824%2900429-X

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