Low carbon dioxide levels improve microbial production of biodegradable plastic

In an innovative gas fermentation process, reducing the concentration of carbon dioxide was found to significantly improve microbial production of the biodegradable plastic poly[(R)-3-hydroxybutyrate]. Researchers found that hydrogen-oxidizing bacteria grown under safe, nonflammable gas conditions enable more efficient production of biodegradable plastic at lower CO₂ levels. The study provides a promising strategy for sustainable carbon recycling and efficient CO₂ utilization.

As efforts to reduce carbon dioxide (CO₂) emissions accelerate worldwide, scientists are exploring ways to transform this abundant greenhouse gas into useful products. One approach is microbial CO₂ conversion, which uses naturally occurring microorganisms to convert CO₂ into sustainable materials. In particular, Ralstonia eutropha (a hydrogen-oxidizing bacterium) is widely used in this process and uses hydrogen, oxygen and CO₂ to synthesize biodegradable plastics such as poly[(R)-3-hydroxybutyrate] (P(3HB)).

Conventional gas fermentation systems often require high hydrogen concentrations in the flammable range, which affects the safety of the process. To address this, a research team from the Institute of Science Tokyo (Science Tokyo), Japan, had previously developed a noncombustible gas culture system.

Now, the group used the noncombustible system to investigate how adjusting the concentration of CO₂ could improve P(3HB) production under safe operating conditions. The study was led by Assistant Professor Yuki Miyahara from the Department of Materials Science and Engineering at Science Tokyo, in collaboration with graduate student Chih-Ting Wang, Postdoctoral Researcher Ramamoorthi M. Sivashankari and Professor Takeharu Tsuge, all from Science Tokyo. The findings are published in ACS Sustainable Chemistry & Engineering.

“We observed that reducing CO₂ concentration resulted in higher production of P(3HB),” explains Miyahara.

Contrary to conventional expectations, the researchers discovered that lowering the supply of CO₂ to approximately 1.4% by volume significantly increased the accumulation of P(3HB) inside the cells. Moreover, the bacteria not only produced more plastic but also converted the CO₂ more efficiently than cultures grown under higher CO₂ concentrations.

To further understand why low CO₂ concentrations improved polymer production, the team investigated the role of carbonic anhydrase (Can), an enzyme that rapidly converts CO₂ into bicarbonate. Since this reaction plays an important role in supplying inorganic carbon for cellular metabolism, the researchers tested whether increasing the enzyme’s activity could enhance P(3HB) production.

The results revealed that increasing Can expression boosted the accumulation of P(3HB), but only under low CO₂ conditions. This suggests that efficient carbon processing within the cells is important when external CO₂ is limited. Increased Can expression ensured an ample supply of inorganic carbon, allowing the cells to produce larger amounts of biodegradable plastic.

“The combined effect of low CO₂ and enhanced Can activity reveals an effective strategy for improving microbial carbon utilization, making it safer and more efficient,” comments Miyahara.

According to the authors, low CO₂ availability triggers adaptive cellular responses that improve carbon utilization efficiency. Therefore, instead of limiting growth, moderate CO₂ scarcity encourages the cells to use available carbon more effectively, resulting in greater polymer accumulation. However, under higher CO₂ concentrations, these adaptive responses become less pronounced because carbon is already readily available.

Overall, the study inspires the development of industrial processes capable of converting low-concentration CO₂ sources, such as exhaust gases, into biodegradable plastics. By combining safer gas handling with improved carbon conversion, the approach offers a promising path for sustainable carbon recycling and reducing greenhouse gas emissions while producing eco-friendly materials.

In the future, the researchers plan to further improve the process and extend this strategy to other microorganisms and products. These advances could accelerate the development of new processes that transform waste carbon into a wide range of renewable materials, supporting the transition toward a circular carbon economy.

Who’s behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

Full profile →

Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

Full profile →