CO2: Feedstock of the future bioprocesses


Author: Özge Ata

Carbon serves as the building block of life, as well as the goods and products we use every day. We consume fossil fuels and use carbon to make plastic and a variety of other products. Life as we know it today would not be possible without it. Therefore, carbon balance is crucial to have a sustainable world and future. In this context, CO2 balance is of particular interest because the rising atmospheric CO2 concentrations due to human activities is the main trigger for global warming, which in turn leads to a climate crisis that affects the global health, economy, and future of our planet.

Microbial CO2 capture for a sustainable future

Fortunately, the solution may be hidden in the problem. Microbial CO2 capture to produce value-added products is emerging as a new field in the fight against the climate crisis by reducing the CO2 levels in the atmosphere.

The use of autotrophic microorganisms that can capture CO2 and produce chemicals is a long-known process. The production of poly(3-hydroxybutyrate) (PHB) by Cupriavidus necator is one of the famous bioprocesses that converts CO2 into PHB, which can serve as an alternative to conventional fossil-based plastics. Many other chemoautotrophic organisms are also used to produce ethanol, 2,3-butanediol, butanol, isopropanol, acetone, or isobutyric acid, which serve as platforms for third-generation (3G) biorefineries.

However, we are not limited to natural microorganisms. With developments in synthetic biology, genome mining, and computational tools, scientists are able to integrate synthetic pathways into different host organisms with superior properties or even design new-to-nature pathways with better carbon capturing efficiency. Two chassis organisms, Pichia pastoris (Komagataella phaffii) and Escherichia coli were recently engineered to grow solely on CO2. Moving one step further, the synthetic P. pastoris strain was shown to be capable of producing organic acids that can be used as building blocks to replace petroleum-based poly-acrylic acids, absorbents, polyesters, plastics, and synthetic fibers using CO2 as a carbon source. These strains need to be optimized to achieve industrially viable production rates, but they are a first step in proving that CO2 can be exploited as a feedstock for chemical production.


Electrochemical conversion of CO2 as a part of green chemistry

Green chemistry is ecologically-oriented chemistry for the sustainable production of chemicals through energy and resource-efficient process design with the aim of waste reduction and recycling. In this context, CO2 can serve as a perfect substrate for the production of green methanol or formate by hydrogenation or electrochemical reduction of CO2. Integrated systems that simultaneously convert CO2 into methanol or formate or other value-added chemicals, thereby providing carbon and energy sources to microorganisms for the production of value-added chemicals have great potential to mitigate the CO2 levels in the fight against the climate crisis.


What is the next step?

Carbon capture and utilization (CCU) is gaining attention and popularity. Researchers are working to develop new technologies that will enable more efficient technologies with better CO2 capture properties and higher productivities. The European Summit of Industrial Biotechnology, which was held in Graz, Austria on 14-16 November 2022, brought together numerous researchers working on CCU to present the latest scientific advancements as well as industrial stakeholders and policy makers. New technologies for microbial CO2 capture, electrochemical reduction of CO2 for conversion to other C1-molecules as clean carbon and energy sources, and production of food ingredients and chemicals from CO2 clearly show that there is a strong push from scientific and industrial actors. Now is the time for policy makers to enact regulations for CO2-based processes to increase the market share and to cooperate with industrial stakeholders and researchers. Raising public knowledge of the products made with CO2 and educating people about CO2-based processes is another crucial issue that has to be addressed. Only then, we can build a sustainable future that brings prosperity to all the inhabitants of our world. References: Gleizer et al. 2019 Gassler et al. 2020 Baumschabl et al. 2022 Liu et al. 2020 Izadi and Harnisch 2022

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