In view of our fruitful cooperation with NJTech_China in expressing strategies at the beginning of the project, we decided to further develop partnership with them throughout our 2022 iGEM project.

    The offline meetup allowed us to have a more comprehensive and in-depth understanding of each other's project. We found that glucose, the very carbon source used by both teams to support the survival of the engineered chassis in the medium, is temporarily unavailable on terrestrial planets. After a short discussion, we unanimously decided the common goal for both teams to be "providing available carbon source required for the engineered chassis in the process of making our projects realistic on terrestrial planets".

    To this end, we jointly determined the research goals and objects at different stages. We separately looked for effective solutions and finally obtained algae lysate that could support the growth of each other's engineered chassis and verified its validity together.

    We found that actually our media were both synthetic ones, which were prepared by sequentially adding accurately weighed high-purity chemical reagents and pure water. As a result, its components and specific amounts are precisely known. Obviously, this does not apply to the terrestrial scenario set by our project, where these chemicals are temporarily unavailable.

    Different from synthetic medium, natural medium is mainly extracted from animal body fluids, tissues or yeast. It features rich nutrition and satisfying culturing needs. For example, the LB medium commonly used in the laboratory to cultivate E. coli is a natural medium, for its main components are peptone (can be regarded as meat extract) and yeast powder (can be regarded as yeast extract).

    Natural culture medium may be a better match for each other's project with a precondition that we are able to find an organism that can adapt to terrestrial environments. Based on this, we put developing a natural medium as the common goal of our research.

    Secondary producers such as heterotrophic E. coli, animals and yeasts are dependent on primary producers for their survival. As far as the terrestrial environment is concerned, we should choose primary producers who can utilize carbon dioxide, water and other basic nutrients to fix solar energy through photosynthesis and synthesize organic substances to be extracted as the raw materials for natural culture media. Therefore, we invariably turned our attention to the blue-green algae (FACHB-469, a non-toxic cyanobacteria incapable of producing cyanotoxins), which have made great contributions to the improvement of the early earth environment. CPU_Nanjing first took on the task of cultivation of the algae.

    CPU_Nanjing's lab excels in biophysics and chemical biology, so we tried both ultrasonic cracking method and chemical algaecides treatment.

    However, all approaches turned out to be a failure: E. coli cannot use sonicated algae lysate, and algaecides are also toxic to E. coli. Meanwhile both teams suddenly realized that there may not be microbes for anaerobic fermentation. The turning point ocurred after we reported our thoughts and results to Dr. Xin Wang, secondary PI of CPU_Nanjing, who asked us why not just cook the algae and feed it to E. coli, just like parents cook meals for their children at home.

    This was absolutely the wow moment of our two teams’ partnership. After boiling, we have found that both crude algae lysate containing cell debris and lysate supernatant free of cell debris can serve as natural media to support E. coli growth. What's more important is that the process is simple and convenient to implement in terrestrial environment, such as converting solar energy into heat for lysing algae.

    After confirming the treating method of algae, that is, the preparation method of a new natural medium, we prepared a batch of lysate supernatant without algae cell debris (which is convenient for the researchers to observe the growth of bacteria with the naked eye), and sent them to different laboratories located in each other’s schools for further tests.

    The validity of this natural medium was perfectly confirmed there. So far, we have solved the carbon source supply problem of the engineered chassis involved in the landing of each other's project on terrestrial planets.

    At the end of our Partnership, we once again came to Nanjing University of Technology, where we met with team NJTech_China. There, team members from both teams spent a pleasant afternoon looking back on the details throughout the whole cooperation process again.