Before we officially started this year's journey, members of the original line-up gathered together and exchanged ideas of launching the project. Since we need members with various skills to fulfill the ultimate goal together, an enrollment program was designed to establish a diverse team.

    To achieve that, an offline interview was organized to absorb team members. Before holding the interview, we discussed the recruitment plan with our PI and prepared a series of materials. During the interview, we met friends with different backgrounds and communicated with them from different perspectives on the topic of synthetic biology. Their professional performance truly impressed us.

    At the beginning of the competition, we organized a series of brainstorms to discuss what to do this year.

    In order to comprehend the profile of phosphorus on terrestrial planets, we conducted a web search as well as literature mining. As far as phosphorus is concerned, there is no shortage of it on these planets, but it is more in the form of phosphite, hypophosphite, or even schreibersite. This is because they are difficult to be further oxidized, even in an oxygen-rich environment like Earth's atmosphere. At the same time, we learned that these above-mentioned compounds are toxic to most Earth's creatures for they are unable to metabolize phosphorus in low oxidation state directly.

    To fully comprehend the role of phosphate in agriculture production, we paid a visit to Changxing County in Huzhou City, Zhejiang Province, where we visited Dr. Zhang from the School of Life Sciences of Zhejiang University. He has been managing a completely phosphate-free experimental field for years to test the effect of phosphate on rice yield. According to his abundant experience, he told us that the plant biomass, meaning height and width, are determined by nitrogen and potassium, while phosphate decides whether the plant can reproduce or not. In another word, no phosphate in, no crops out.

    Dr. Jierong Jiang, vice director of Jiangsu Institute of Textile Product Quality Supervision and Inspection, warmly received us. We learned from her that the production of natural fibers from biological sources used in textiles, such as cotton, hemp, silk and wool, is obviously dependent on phosphate. We would have to turn to petroleum if there is no phosphate because over 90 percent of chemical fiber comes from oil. In addition to producing raw materials, phosphate is also required by processes such as printing and dyeing, which again emphasizes the role of phosphate in textile industry.

    After confirming the value of the project, the team also needs to confirm the biotechnological feasibility. For this purpose, we visited Dr. Xin Wang from the Faculty of Science, China Pharmaceutical University, whose main research interest during PhD was the production of polyphosphate with Citrobacter freundii as the chassis. He told us that though it is technically feasible from the perspective of synthetic biology, this project is still extremely challenging. The reason lies in the small amount of phosphate required in the growth of bacteria and that phosphate in the process of ATP regeneration can be recycled. That means even if phosphite dehydrogenase is overexpressed in bacterial cells, in theory, they will not continuously oxidize environmental phosphite since it’s futile to produce more phosphate than needed. Therefore, coupling phosphite oxidation to other metabolic pathways in order to make the bacteria stay “phosphorus starving” may be a choice worthy of consideration. In this way, it’s possible to force the bacteria to “manufacture phosphate” continuously.

    In order to deal with the problem of supplying carbon source for engineered bacteria on terrestrial planets, we went to College of Resources and Environment Sciences, Nanjing Agricultural University for help. There, we visited Dr. Xiaomeng Wang whose research orientation is biogeochemical cycle of elements and the relationship between nutrients and water blooms. We described the problem we were facing in detail and she quickly got our key points. She suggested that the blue-green algae, an autotrophic bacterium capable of utilizing solar energy to convert carbon dioxide into organic biomass, may worth a try. The blue-green algae has an origin of around 3 billion years. Their photosynthesis ability contributed to the most critical event in the evolution of the earth: the oxidation of Earth's atmosphere. She continued, “Nevertheless, feeding the blue-green algae toE. coli is a problem for you to solve, because no one has ever done this before.”

    Since we aimed to manufacture phosphate, HP members organized a discussion with other teammates about how to obtain the final product after the overall feasibility was initially verified. All members agreed that at least a bench-scale test should be performed. As we need corresponding devices to simulate production process, we went to Nanjing Organic Glass Factory and visited manager Zheng, who has been long dedicated to handcrafting small production equipment for universities and research institutions. We communicated with manager Zheng about the design concepts and application requirements of our Hardware. Soon we obtained a prototype of Hardware which integrated parts handcrafted by workers and modules (such as solar panel, battery and heater) built by our team.