The ocean, Earth’s largest natural carbon sink, absorbs over a quarter of human-caused carbon dioxide emissions annually, effectively mitigating global warming. However, ocean acidification, triggered by the continued absorption of carbon dioxide by seawater, poses a serious threat to marine ecosystems. Converting this carbon that has already entered the ocean into a usable resource and mitigating ocean acidification are common challenges in promoting the development of the “blue economy” and achieving the “dual carbon” goals.
A team led by Gao Xiang from the National Key Laboratory of Quantitative Synthetic Biology and the Institute of Synthetic Biology at the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, in collaboration with a team led by Xia Chuan from the University of Electronic Science and Technology of China, has for the first time proposed and validated an “artificial ocean carbon cycle system” based on a coupled electrocatalysis-biocatalysis strategy. This system captures carbon dioxide from natural seawater and converts it into intermediates that can be directly incorporated into biomanufacturing, and then further upgraded into a variety of high-value chemicals and materials. Using biodegradable plastic monomers as a demonstration case, this research holds the potential to provide a biomanufacturing platform for a wider range of products, including fuels, pharmaceuticals, and food ingredients. The results were recently published in the international academic journal Nature Catalysis.
The first key step in the research was led by Xia Chuan’s team at the University of Electronic Science and Technology of China. They used electrocatalytic technology to achieve efficient carbon capture from seawater. Facing challenges such as electrode passivation and salt deposition, the team designed a novel electrolysis device. Experimental results showed that the device could operate stably and continuously in natural seawater for over 500 hours, achieving a CO2 capture efficiency exceeding 70% and simultaneously producing hydrogen as a byproduct. The team also successfully developed a highly active and highly formic acid-selective bismuth-based catalyst, which efficiently converts captured CO2 into formic acid through electrocatalysis, consistently producing a high-concentration formic acid solution.
The second key step in the research was led by Gao Xiang’s team at the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences. They used biocatalysis to convert formic acid solution into biochemicals that can replace fossil fuels. The team selected the extremely fast-growing marine bacterium Nasturtium and, through long-term laboratory evolution and synthetic biology, systematically reconfigured the bacterial genome, successfully engineering a strain capable of tolerating high formic acid concentrations and efficiently growing and metabolizing it using it as a sole carbon source. The engineered bacteria can accurately convert formic acid into succinic acid, the core monomer of the synthetic biodegradable plastic polybutylene succinate (PBS), and lactic acid, the monomer of the biodegradable plastic polylactic acid (PLA).
To verify the carbon flow and industrial feasibility of the entire system, the researchers conducted carbon isotope labeling experiments, confirming that the carbon atoms in the resulting succinic acid molecules originated from the initially captured CO2. Furthermore, they completed scale-up experiments in 1-liter and 5-liter fermenters, successfully transitioning the research from laboratory shake flask to pilot-scale. Notably, the production of lactic acid in these experiments also offers new possibilities for expanding the diversity of biodegradable plastics.
Currently, the research team has further synthesized fully biodegradable PBS and PLA based on the synthesized bioplastic monomers and produced a demonstration straw product, demonstrating the industrial feasibility of converting seawater into green materials. The researchers note that through modular design and combinatorial optimization of electrocatalytic and metabolic pathways, the platform has the potential to be expanded to a diverse product portfolio, including organic acids, monomers, surfactants, and nutritional ingredients, serving industries such as materials, chemicals, pharmaceuticals, and food.
