Bacteria turns atmospheric CO2 into bioplastics with promising applications

As researchers suggested, high-efficiency electrode catalysts and systems are actively being developed for the effective conversion of CO2. Only compounds with one or up to three carbon atoms are occasionally created as conversion products.

One-carbon compounds like CO, formic acid, and ethylene are created with a comparatively high level of efficiency. These systems can also create liquid molecules with multiple carbons, such as ethanol, acetic acid, and propanol, although there are restrictions on conversion efficiency and product choice due to the nature of the chemical reaction, which needs more electrons.

Using "Cupriavidus necator"

The team has created a two-part method that uses the bacterial species Cupriavidus necator to convert CO2 into a typical sort of bioplastic. The ability of C. necator to create carbon compounds from other carbon sources, such as poly-3-hydroxybutyrate, or PHB, a form of biodegradable and compostable polyester, is widely known.

C. necator consumes the formate feedstock produced by the electrolytic reaction and accumulates PHB granules, which can later be recovered from harvested cells. The study's authors are confident that their method is scalable and has the potential to significantly alter the production of plastics.

"The results of this research are technologies that can be applied to the production of various chemical substances as well as bioplastics and are expected to be used as key parts needed in achieving carbon neutrality in the future," they said.

The team claims that as long as the bacterial cells are replaced every day, and the plastic product is taken out to maintain the reactions, their system can run continuously.

Study abstract:

Converting anthropogenic CO2 to value-added products using renewable energy has received much attention to achieve a sustainable carbon cycle. CO2 electrolysis has been extensively investigated, but the products have been limited to some C1-3 products. Here, we report the integration of CO2 electrolysis with microbial fermentation to directly produce poly-3-hydroxybutyrate (PHB), a microbial polyester, from gaseous CO2 on a gram scale. This biohybrid system comprises electrochemical conversion of CO2 to formate on Sn catalysts deposited on a gas diffusion electrode (GDE) and subsequent conversion of formate to PHB by Cupriavidus necator cells in a fermenter. The electrolyzer and the electrolyte solution were optimized for this biohybrid system. In particular, the electrolyte solution containing formate was continuously circulated through both the CO2 electrolyzer and the fermenter, resulting in the efficient accumulation of PHB in C. necator cells, reaching a PHB content of 83% of dry cell weight and producing 1.38 g PHB using 4 cm2 Sn GDE. This biohybrid system was further modified to enable continuous PHB production operated at a steady state by adding fresh cells and removing PHB. The strategies employed for developing this biohybrid system will be useful for establishing other biohybrid systems producing chemicals and materials directly from gaseous CO2.