Descriptions

Inspiration

Severe climate crisis:

    Over the past century, the burning of fossil fuels, coupled with unequal and unsustainable utilization of energy and land, have brought about continuous global temperature rise. The climate crisis has become one of the greatest challenges to human development in the 21st century. According to media reports, Canadian wildfires triggered by climate change have been ongoing for over 5 months, with a total burnt area exceeding 180,000 square kilometers. By the end of September, approximately 900 areas are still ablaze, leading to the evacuation of more than 200,000 people and the tragic loss of 8 firefighters.

(Figure 1 Canadian wildfires)

    
    The Intergovernmental Panel on Climate Change (IPCC) released the "Climate Change 2023" report, which states that greenhouse gas emissions have caused a global average temperature increase of 1.1°C. This has resulted in more frequent and intense extreme weather events, bringing the nature and human population in various regions worldwide increasingly in risk.

(Figure 2 Reports about the global warming caused by human activities)

Solution:

    
    In order to tackle the climate crisis, the world must accelerate the search for alternative new energy sources and move away from fossil fuels. Currently, the new energy sources, such as hydropower, wind power, solar power, tidal power and nuclear power, are heavily limited by the environmental conditions. In 2023, due to the storage and handling issues of nuclear waste, Japan will release a large amount of nuclear wastewater into the ocean, which may cause serious pollution to the marine environment.

    To address these issues, our focus has turned to biofuels. In recent years, different microbial cells have been developed and utilized to synthesize drugs, biobased materials and chemicals; it is now their time to shine.

SAF (Sustainable Aviation Fuel) - The Skyway to the Future:

    
    According to reports from IPCC, the aviation industry's greenhouse gas emissions accounted for approximately 1.8% of global emissions in 2019, with emissions from Chinese flights accounting for 13% of the total. Aviation fuel is one of the main sources of greenhouse gas emissions in the aviation industry. To protect our planet, the International Air Transport Association (IATA) has proposed that the airline must reduce CO2 output and achieve net-zero carbon emissions no later than 2050. To achieve the target, sustainable aviation fuel (SAF) is considered one of the most more viable and scalable option.

(Figure 3 Manufacturing process of SAF)

    
    SAF is a lower-carbon alternative to fossil-based fuel that is made from renewable feedstocks, such as used cooking oil, municipal and agricultural waste. SAF can be blended with fossil aviation fuel at a ratio of up to 50%, effectively reducing carbon emissions in the aviation industry. From raw material extraction, processing, transportation to final use, SAF can reduce lifecycle carbon emissions by up to 80% to 85% compared to the traditional aviation fuel. This is because traditional fossil fuels emit carbon dioxide, while sustainable aviation fuel generally refers to materials obtained from various sustainable sources (biomass or synthetic) through chemical reactions. It recycles carbon dioxide by utilizing the stored carbon in biomass materials, thus achieving carbon circulation. In addition, the advantage of sustainable aviation fuel is reflected in its minimal ecological impact. Its production process does not affect food production, soil fertility, or biodiversity.

(Figure 4 Advantages of SAF)

    
    Isobutanol, as a four-carbon branched-chain alcohol, has several advantages over traditional biofuels such as ethanol and n-butanol, including high energy density, high octane number, easy miscibility, low vapor pressure, low hygroscopicity, and low corrosion. It can be directly used in existing engines and other fuel utilization equipment, or can be transported through existing gasoline pipelines and distribution channels. Therefore, it is considered as a promising new generation biofuel that can replace gasoline. Furthermore, isobutanol can also be used as a promising precursor for renewable SAF production via the Alcohol-to-Jet fuel technology.

Our Project

Our bacterial strains:

    
    Zymomonas mobilis is a facultative anaerobic bacterium that is initially isolated from pulque in Mexico. It is the only currently known gram-negative bacterium that metabolizes the sugars via the Entner-Doudoroff (ED) pathway under anaerobic conditions for ethanol production, and exhibits several excellent characteristics such as high glucose uptake rate, high apparent yields of ethanol from sugars and high ethanol tolerance. In addition, Z. mobilis is generally regarded as safe (GRAS). The high ethanol-producing ability of Z. mobilis also provides it with natural excellent resistance to alcohol compounds. All these advantages make Z. mobilis to be a promising microbial cell factory for isobutanol production and we select it to be involved in our project.

Zero-carbon SAF:

    
    Our project aims to construct bioparts associated with isobutanol biosynthesis in Zymomonas mobilis. These parts will be characterized and assembled to build the isobutanol production module in Z. mobilis using the CRISPR-Cas gene editing technology and homologous recombination technology. In addition, in order to further increase the isobutanol yield in Z. mobilis, the Calvin cycle pathway coupled with a heterologous carboxysome for CO2 concentrating and CO2 fixation will be transformed as well. Thus, the CO2 released during the isobutanol fermentation process can be absorbed and further transformed into isobutanol again, achieved an efficient zero-carbon isobutanol generation.

(Figure 5 Zero-carbon isobutanol biosynthesis)

    
    Our project is concentrating on the environmental-friendly isobutanol (precursor of SAF) production through the synthetic biology technology.

    The successful implementation of our project will not only establish the basic and composite bioparts for non-model microorganisms (Z. mobilis) but also allow the efficient microbial isobutanol production. We hope the microbial isobutanol here would finally replace the chemical fossil fuel to the maximum in the future, making the airline clean, protecting the environment, and promoting the sustainable development.