A team of researchers that included doctoral student FUJIWARA Ryosuke, Associate Professor TANAKA Tsutomu (both from the Graduate School of Engineering of Kobe University) and Research Scientist NODA Shuhei (from RIKEN Center for Sustainable Resource Science), has successfully improved the production of target chemicals from biomass.
The researchers achieved this breakthrough by metabolically engineering the bacteria utilized in bio-production. This approach would allow the microbes to use different types of sugars that are absorbed from the biomass for different purposes.
However, difficulties were encountered when microorganisms were used to generate target chemicals, such as the production of the target chemical reduces when the bacteria utilize the sugars or carbon sources for their own propagation. By contrast, when this propagation is suppressed, it weakens the pathogens and leads to an overall reduction in production.
In an effort to overcome this problem, the scientists came up with a new method known as Parallel Metabolic Pathway Engineering (PMPE). This strategy enables the researchers to regulate the production of target chemicals in addition to the propagation of microorganisms. The team utilized this method to modify Escherichia coli bacteria to effectively increase the production of muconic acid—the nylon precursor.
If the chosen carbon source is potentially used only for the production of target chemicals and if the remaining sources are used for the propagation of microbes, there would be significant developments in the production of raw materials and aromatic compounds for chemical and medical products. The study results were initially published in the Nature Communications journal on January 14th, 2020.
- The development of the PMPE approach, which enables the usage of sugars for the production of target chemicals and the propagation of microbes, should be controlled separately. With this strategy, the scientists effectively boosted the production of the target chemical—muconic acid.
- The PMPE strategy can be used for producing numerous raw materials like dicarboxylic acid and aromatic compounds, which are used in medicines and chemical products.
- Predicted to enhance the effective usage of raw materials, like biomass, which include different types of sugars.
Fossil fuels are mainly used as raw materials for creating a wide range of products. But the production of compounds derived from petroleum raises the amount of CO2 in the atmosphere, resulting in a host of environmental issues like global warming.
As a result, biorefinery technologies should be developed in which microorganisms are used to create chemical compounds from renewable resources, such as tree and plant matter, that are abundant in nature.
Products derived from biomass have the benefit of being carbon neutral—that is, they do not boost the quantity of atmospheric CO2. It is believed that the use of biomass for producing many useful compounds can lay a foundation for a low-carbon society, thereby decreasing the quantity of CO2 in the atmosphere.
Muconic acid is a handy chemical that can be easily changed into adipic acid, a kind of ingredient used in the production of nylon. Muconic acid is also utilized as a raw material for producing a range of chemical and medical products.
However, at present, this acid is chemically produced from petroleum resources. It is believed that a fermentation technique can possibly be devised using pathogens and plant-based renewable resources that have fewer by-products and milder reaction conditions.
But microbes make it difficult to create the required chemicals from biomass. In fact, there are several cases where despite using the biomass, the microbes propagate themselves and do not produce the target chemical.
Yet, modifying the metabolism to prevent the multiplication of microbes tends to weaken them, which means it is not possible to synthesize the target chemicals. The balance between the production of target chemicals and the self-propagation of microbes is a major problem.
To overcome this problem, the scientists devised a method known as PMPE, where they isolated the utilization of sugars between the production of target chemicals and the propagation of microbes. This method enabled the team to regulate each process separately.
Lignocellulosic biomass is composed of xylose and glucose sugars. It does not contend with global food supplies. The scientists devised a metabolic strategy in which the E. coli bacteria are altered such that they would use glucose for the production of target chemicals and xylose for the propagation of microbes.
In typical pathogens, both xylose and glucose sugars utilize the same metabolic pathway and both are used for growing microbes and synthesizing target chemicals. This decreases the quantity of the target chemical produced because the microorganisms absorb the sugars to create and sustain the energy and elements they need to survive.
To reduce this problem, the scientists thus developed the new strategy called PMPE. Splitting the metabolic pathway of the microbes enables each sugar to be used separately with all the xylose being utilized for the propagation and maintenance of microbes and all the glucose being utilized for the production of target chemicals. This resulted in higher production of the target chemical because none of the glucose was being used for the growth of microbes.
The scientists introduced a metabolic pathway to the altered E. coli bacteria for producing muconic acid. The altered E. coli bacteria used the xylose and glucose sugars, resulting in the yield of the target chemical.
The scientists successfully produced 4.26 g/L of muconic acid with a yield of 0.31g/g-glucose. This is believed to be the world’s highest yield, demonstrating the effectiveness of the PMPE approach.
The scientists then analyzed whether the PMPE approach can potentially be used for producing target chemicals apart from muconic acid. Consequently, the team effectively boosted the yields of 1,2-propanediol, which is utilized as an additive in food products and medicines, and the essential amino acid and aromatic compound called phenylalanine. These outcomes have demonstrated that PMPE is a multipurpose method that can be efficiently used for producing a wide range of compounds.
It is believed that the PMPE approach devised by the scientists can be used to boost the yield of a wide range of raw materials, like dicarboxylic acid and aromatic compounds, that are utilized in chemical and medical products. The PMPE technique of modifying the metabolism of microbes will enable the efficient utilization of biomass containing multiple sugars.
The study was supported by the Japan Science and Technology Agency (JST)’s Mirai program: Small start-type (feasibility study) “Realization of a Low Carbon Society, a global issue”: Realization of a low carbon society through game-changing technologies. Research title: “Creation of PEP-accumulating chassis strains by cell surface engineering and metabolic engineering” (Grant No. JPMJMI17EI).
Additional support was offered by Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (B) (Grant No. 19H02526); RIKEN Center for Sustainable Resource Science, Special Postdoctoral Researcher Program; and Grant-in-Aid for JSPS Research Fellows.