Questneers : Sang Yup Lee (KAIST), SangWoo Seo (Seoul National University)
As the climate crisis becomes more serious, voices are rising that the modern industrial structure dependent on fossil fuels must be transformed into a sustainable industrial structure using renewable raw materials. As an alternative, systems metabolic engineering and synthetic biology technologies that produce useful chemicals by manipulating microbial metabolic pathways are receiving attention. Can we develop microbial cell factories that produce plastics more competitively than petrochemical processes using greenhouse gases as raw materials?
Attempts to replace fossil fuels are being made in various fields worldwide. The rapidly growing systems metabolic engineering and synthetic biology show the potential to transform traditional petrochemical processes dependent on fossil resources into bio-based processes. To date, there are various cases of producing useful substances through microbial cell factories. The scientific possibility of efficiently producing useful chemicals such as plastics using greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄), which are the main culprits of climate change, as main raw materials has been raised for a long time. However, it faces various technical challenges to achieve industrial competitiveness.
Strain development that can produce plastics using greenhouse gases as carbon sources is one of the core challenges. Particularly, since carbon dioxide has no delocalized electrons, reducing power such as hydrogen (H₂) or formic acid (FA) must be provided for microorganisms to utilize it. Therefore, research is being conducted to improve microorganisms that naturally grow by consuming greenhouse gases (e.g., Cupriavidus necator, Methylocystis parvus) or to improve well-known strains to utilize greenhouse gases. However, to increase the speed and efficiency of this conversion process, the difficulty of finding or improving enzymes that play key roles is accompanied.
What steps to control when optimizing metabolic pathways of selected strains is also a difficult problem. The most commonly attempted method is to target and optimize rate limiting steps. As part of such methods, there are cases where specific steps of the tetrahydrofolate (THF) cycle and glycine cleavage (GCV) cycle in Escherichia coli were manipulated to grow in environments with only carbon dioxide and formic acid. However, since the growth rate is significantly lower compared to glucose and the productivity of produced substances is also low, more efficient metabolic pathways and strains must be created in the future.
Another difficulty arises from the complexity of living organisms. In living organisms, thousands of reactions occur simultaneously among hundreds of proteins. Therefore, in the process of supplying carbon dioxide to microorganisms as food to produce desired substances, numerous substances and reactions are complexly involved, making it difficult to achieve production as efficiently as theoretically expected. To solve this, research on known unknowns that are known to be involved in this production process but whose functions have not been revealed, as well as continuous research on unknown unknowns whose existence itself is not yet known, is necessary.
Recently, attempts are being made to solve this problem using artificial intelligence-based protein structure prediction technology, but since there are too many substances to analyze and the pathways they affect are too complex, it still takes a long time. To reduce this verification time, innovative tools in systems metabolic engineering and synthetic biology fields must emerge, and utilization of biofoundries that can increase the speed and accuracy of verification experiments is essential. Furthermore, to secure commercial competitiveness of microbial cell factories, it must be determined where and how to supply feedstock, and since it must be scaled up from lab-scale to large-scale, convergence research encompassing knowledge from various fields is absolutely necessary.
If plastics widely used in our daily lives can be efficiently and competitively produced using greenhouse gases such as carbon dioxide and methane as raw materials through microbial cell factories, it will be possible to respond to climate change by replacing a significant portion of the existing petrochemical industry, and it will be an opportunity for South Korea to create new industries based on sustainable manufacturing technology.