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Bioplastic Production: Bacteria Convert Carbon Dioxide from Air


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A well-known bacterium can convert carbon dioxide from the air into bioplastic, solving two global problems in one quick step using a prototype system developed by Korean chemical engineers.

Plastic-eating bacteria, capable of breaking down plastic waste in a matter of hours, has recently gained a lot of attention as a microscopic solution to the world’s growing plastic problem.

While cleaning up the mess we’ve already created is a big priority, finding new ways to produce plastic from sources other than crude oil and its derivatives is also vital to reducing our dependence on fossil fuels. Plastic polymers are long chains of repeating subunits linked together, and these chains are often based on carbon atoms.

Many chemical engineers have the brilliant idea that rising levels of carbon dioxide in the Earth’s atmosphere could be a untapped resource for making plastics or other carbon-based products like jet fuel or concrete, if only we could capture carbon dioxide from the atmosphere. . air and make something out of it.

One way to convert carbon dioxide into other useful carbonaceous compounds is to introduce electricity into a reaction called electrolysis. But this method, while promising, yields mostly short-chain starting compounds of one to three carbon atoms. Creating chemicals with carbon chains longer than those of carbon dioxide is a more complex and efficient task.

In this new work, a team of chemical engineers from the Korea Advanced Institute of Science and Technology (KAIST) has developed a two-component system to convert carbon dioxide into a common type of bioplastic using a bacterium called Cupriavidus necator. The first step in the system is the electrolyser, which converts carbon dioxide gas to formate. It is then fed into a fermentation tank where the bacteria work.

C. necator is known for its ability to synthesize carbon compounds such as poly-3-hydroxybutyrate or PHB, a type of biodegradable and compostable polyester, from other carbon sources.

In this case, C. necator consumes the formate raw material from the electrolysis reaction and the initial PHB pellets, which can then be extracted from the harvested cells.

The same solution circulates between the electrolysis reaction and the fermentation tank with a membrane separating the two chambers so that the bacteria are isolated from the by-products of the electrolysis reaction.

And if the system is powered by renewable energy sources, it could be a way to produce bioplastics without using fossil fuels, which simultaneously uses carbon dioxide, which needs to be quickly removed from the air to reduce global warming.

Hongju Lee and Sang Ip Lee, the biomolecular engineers at KAIST who led the study, are optimistic that their approach can be scaled up and could somehow help change the way plastics are made.

“The results of this study are technologies that can be applied to the production of various chemicals in addition to bioplastics and are expected to be used as key elements needed to achieve carbon neutrality in the future,” they say.

Laboratory experiments have shown that C. necator cells in a hybrid system can synthesize such an amount of PHB that the polyester product makes up to 83% of the dry mass of bacterial cells after 120 hours or 5 days of operation.

Based on these results, the researchers claim their setup is up to 20 times more productive than similar systems previously tested.

The team also reported that their system can run without interruption as long as the bacterial cells are replenished each day and the plastic product is removed to keep the reaction going.

This continuous production will be the key to making the system work at an industrial level. So far, researchers have tested it in just 18 days and produced 1.45 grams of polyester.

But the researchers say their integrated system is an improvement over previous batch reactors or other plants that could only run one reaction stage at a time and required additional separation and purification steps.

Meanwhile, other biochemical engineers are looking to improve C. necator’s natural ability to produce PHB from carbon dioxide through some genetic modifications because they say the amount of polymer produced by C. necator is still too small to be marketed – according to at least for now.

The study is published in PNAS.

Source: Science Alert

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