Our team members learned through casual literature research that microplastics are quietly entering the human body. Recently, Nature reported that microplastics can cause cerebral thrombosis, and another study suggested that they are related to Parkinson's disease. As such, the connections between microplastics and various human diseases are being continuously revealed.

After further reviewing the literature, we discovered that microplastics are not only associated with inflammatory bowel disease and fetal developmental abnormalities, but more importantly: diet is the main way for the human body to intake microplastics, and intestinal absorption is the key entry point for them to enter the bloodstream and cause harm to the entire body. At the same time, here, microplastics will scratch the intestinal wall and damage the microbiota, laying hidden dangers for subsequent systemic damage.

Therefore, our approach is clear: 1. Block at the source, directly degrade microplastics in the intestines; 2. At the same time, repair the damaged intestinal microbiota to safeguard the body's first line of defense.

We conducted a literature search and discovered that the relevant PET enzymes can help us achieve this goal. However, the expression of this degrading enzyme needs to take place within eukaryotic organisms. Considering the characteristics of the intestinal microenvironment, we need to select specific chassis microorganisms that meet the requirements. Among them, Saccharomyces cerevisiae quickly caught our attention. It has two significant advantages: one is that it has GRAS certification and has been used in the food and pharmaceutical industries for many years, with good safety; the other is that the tools for genetic modification are very mature, and there have been successful cases of it secreting complex proteins before, which exactly meet our needs for it to express two degrading enzymes. Therefore, we planned from the very beginning to use Saccharomyces cerevisiae as the sole chassis microorganism, to build a complete path from "colonization of the strain in the intestine → secretion of degrading enzymes → degradation of microplastics". Thus, our project officially began.

Fig 3. Our Topic Selection Strategy

In order to more effectively degrade the microplastic particles in the human intestinal tract and block the main pathways through which microplastics enter the body, we chose a degradation and treatment system based on yeast. Before delving deeper into our research ideas, we conducted a detailed background investigation of the project.

In order to gain a deeper understanding of the public's awareness and attitudes towards the hazards of microplastics, we conducted a specialized questionnaire survey. Through a systematic analysis of the data from 114 respondents, it was found that the overall situation of the public on this issue is "a preliminary awareness has been established, but there is a significant gap in deep understanding and systematic knowledge." The public generally shows concern about microplastics, which also reflects the vague understanding of the related hazard mechanisms. This reality highlights the necessity and urgency of our project research.

Fig 4. Basic information survey

We will further optimize our project based on the survey results, and at the same time, we will strive to promote systematic countermeasures against microplastic pollution through scientific exploration and public education, in order to make concrete efforts to safeguard human health. Although there are still many challenges ahead, we will maintain firm confidence, continue to work hard, and strive to ensure that the project outcomes make a practical contribution to the health of all humanity worldwide.

Fig.5. Basic understanding of microplastics

In recent years, due to the extensive use of plastic products and improper disposal, microplastic pollution has gradually evolved into a global environmental issue. These microplastics are everywhere and can enter the human body through various pathways and accumulate within it. They not only have the potential to cause damage to various tissues and organs, but also may have toxic effects, posing a serious threat to human health.

Our research originated from concerns about the risks of microplastics to human health. To address this issue, our team plans to utilize synthetic biology technology to develop an engineered yeast that can specifically remove microplastics from the human gut. In the initial stage of the research, we conducted a questionnaire survey to gain a deep understanding of the public's awareness and actual needs. These findings provided crucial guidance for our research, pointed out the direction, and determined the key points from the technological development to the exploration of practical applications.

Fig 6. The true view on the microplastic issue

Our public survey provided clear and encouraging guidance on the direction of this project. The public generally concerns the issue of microplastics and shows a strong willingness to jointly address this health threat. They achieve this goal by changing their own habits and supporting the development of new technologies. In the open-ended questions, many respondents mentioned that they hope to gain a deeper understanding of the hazards and prevention knowledge related to microplastics through various means, such as popular science articles, expert interpretations, and social media. It is worth noting that after introducing an innovative solution, "an engineered yeast system for degrading microplastics", although the public expressed expectations, they also candidly raised concerns about its safety. These feedbacks not only confirmed the significance of our research but also indicated that the next steps should focus on strengthening scientific communication, ensuring transparent communication of product information, and investing more effort in the safety design of engineered bacteria.

Fig 7. In-depth views and open opinions

Therefore, we have completed the entire cycle process from identifying problems to verifying the project's value, and this questionnaire survey has become the crucial first step in building this closed-loop understanding. Not only did we reveal the superficial phenomenon of the public's "insufficient understanding" of microplastics, but we also precisely pointed out the deficiencies of our project in certain specific aspects. These insights provide guidance for our subsequent actions. By revealing the positive attitude of the public towards solving the problem of microplastics, this survey indicates that the implementation of effective and safe microplastic degradation intervention measures in the human intestinal tract has received widespread recognition and significant social value from the public.

In addition to optimizing our project itself and analyzing the questionnaire survey, the promotion, education and scientific dissemination regarding microplastics are also of great significance. These efforts have played a positive role in facilitating the in-depth development of our project. Our team has been actively involved in scientific dissemination and educational promotion activities to raise public awareness. Through knowledge sharing and transparent explanations of the product development process, we are committed to enhancing the public's understanding of microplastic pollution. We firmly believe that education is the first step towards scientific progress and problem-solving.

At the beginning of the project, we conducted an analysis of the potential stakeholders of this project and utilized Mendelow's matrix to assist us in planning. The results of this analysis will guide our subsequent comprehensive human practices.

Fig 8. Mendelow's matrix of our project.

After the initial conception, our project aims to enable the degradation of microplastics in the intestinal tract. To achieve the sensing of microplastics, we hope to simulate the conditions where microplastics exist. However, after conducting literature and database searches, we have not found any corresponding promoters for microplastics. Thus, how to sense microplastics has become a challenge.

We hope to explore alternative methods to detect the presence of microplastics, or other corresponding mechanisms that can help us degrade microplastics at a regular interval.

We had an exchange with the team from Jiangnan University. During the exchange, inspired by their project ideas, our team used multiple promoters to simulate the intestinal environment and carried out constitutive expression, rather than simply responding to microplastics.

After reviewing the literature, our team employed three types of promoters (glucose promoter, copper ion-induced promoter, and hypoxia promoter) in combination with quorum sensing to regulate the expression of microplastic-degrading enzymes.

Fig 9. The exchange activities with Jiangnan University

Fig 10. Alternative solutions for detecting microplastics

As the research progressed, we found that a single strain could not simultaneously meet the three core requirements: "safety, intestinal colonization ability, and efficient enzyme expression." Starting with Saccharomyces cerevisiae—our initial candidate—while it indeed excels in safety and engineerability, both literature reviews and our preliminary colonization simulation experiments revealed that it cannot persist long in the intestines or survive for an extended period. Consequently, even if it could secrete degrading enzymes, the duration would be insufficient to achieve long-term degradation, which became its critical shortcoming.

We also attempted to evaluate other candidate bacteria, but the results all fell short of expectations:

- E. coli Nissle 1917 has mature modification tools and high expression efficiency, but public acceptance of "E. coli" is low, and it also fails to colonize the intestines long-term;

- Bifidobacterium is safe and capable of colonization, but it is a strict anaerobe, making cultivation and modification extremely difficult with limited available tools;

- Bacteroides has strong colonization ability, but its modification tools are immature, and the safety of some strains remains uncertain;

- Clostridium has diverse metabolic functions, but some strains produce toxins, making risk control impossible;

- Ordinary Lactiplantibacillus plantarum is food-grade and tolerant to acid and bile salts, but it lacks sufficient modification tools, has low expression efficiency, and cannot even support complex genetic circuits.

After evaluating all options, every single strain had obvious shortcomings and could not fully meet the comprehensive needs of intestinal microplastic treatment, causing our research to come to a standstill.

Fig 11. Analysis of the original plan

Unable to resolve the issue of using a single strain, we decided to consult Professor Chen Ruibin, an expert in the field of microbial symbiosis.

Professor Chen reminded us not to focus solely on "a single strain working alone." He explained that many microorganisms in nature rely on symbiosis to assist each other—for example, some provide nutrients, while others offer protection, and their collective capabilities are far stronger than when they exist alone. He suggested we shift our mindset and try a "multi-strain symbiotic system," assigning the requirements of "safety, colonization, and expression" to different strains so that they could complement each other’s shortcomings and achieve the goal through synergy. His advice immediately clarified our thinking—we realized we did not have to rely on one bacterium to solve all problems; two bacteria working with divided responsibilities might achieve an "1+1>2" effect. After that, we shifted our research direction from "single chassis bacterium" to "construction of a symbiotic system."

Fig 12. Interview with Professor Chen Ruibin

Fig 13. The conception of a symbiotic system

After deciding to develop a symbiotic system, we reviewed numerous literatures on bacterial symbiosis, adhering to the principles of "safety, synergy, and functional matching." We focused on analyzing whether different strains could coexist peacefully and assist each other.

In further literature research, we identified a specific strain: Lactiplantibacillus plantarum DT88. Previous studies have shown that it can survive long-term in the intestines and has the ability to adsorb microplastics—highly aligned with the goals of our project.

Regarding the symbiotic system, we initially considered including E. coli. However, literature indicated that Lactiplantibacillus secretes organic acids to lower the environmental pH and competes for nutrients and space, which inhibits the growth of E. coli—making the formation of a stable symbiotic system impossible. Thus, we quickly ruled out combinations involving E. coli. Later, we found multiple studies demonstrating a natural symbiotic and mutualistic relationship between Saccharomyces cerevisiae and Lactiplantibacillus plantarum:

- Saccharomyces cerevisiae secretes amino acids such as glutamine and threonine, which serve as "food" for Lactiplantibacillus plantarum (which requires these amino acids for growth);

- In return, Lactiplantibacillus plantarum decomposes complex carbohydrates (e.g., lactose) that Saccharomyces cerevisiae cannot use directly into monosaccharides, which the yeast can utilize.

Moreover, the stability of the entire community improves when they grow together. This perfectly matched our needs, so we finalized the symbiotic combination direction as "Saccharomyces cerevisiae + Lactiplantibacillus plantarum."

Fig 14. Literature verification and strain determination

After confirming that Lactiplantibacillus plantarum would partner with Saccharomyces cerevisiae, we screened specific strains within the Lactiplantibacillus plantarum genus and ultimately selected Lactiplantibacillus plantarum DT88 (hereafter referred to as DT88). This choice was primarily based on its strong alignment with our research goals in several aspects:

First, it has the ability to adsorb microplastics—previous studies have confirmed that it can capture microplastics in the intestines and promote their excretion. This allows it to work with the degrading enzymes secreted by Saccharomyces cerevisiae to form a "adsorption + degradation" dual effect, achieving better results; additionally, it is a food-grade probiotic that can help improve the intestinal environment.

Second, it is highly "robust"—it can withstand gastric acid at pH 2.5 and tolerate bile salts, enabling it to reach the middle and lower intestines (where microplastics primarily act) in a viable state by passing through the stomach and upper small intestine. This solves the common problem of many probiotics "failing to survive the stomach" and eliminates the need for us to develop additional protection methods.

Based on all previous research, we finally confirmed the "Saccharomyces cerevisiae + DT88" dual-strain symbiotic system and clarified their respective responsibilities.

Fig 15. The advantages of the symbiotic system

In the previous questionnaire survey, we learned that the public was concerned about the issue of microplastics. However, due to a lack of sufficient knowledge, they were unaware of the solutions to this problem. We hope to better promote the popular science knowledge about microplastics. Therefore, we have created popular science articles and illustrations.

In order to further promote the project and disseminate knowledge about microplastics, we communicated with Dr. Fang Xin, the managing director of Titanium Capital, and presented our scientific articles and illustrations, hoping to obtain new ideas for the interactive format of our project.

Dr. Fang emphasized the significance of streaming media, videos, etc. Moreover, science popularization should not be limited to the daily protection against microplastics. We can also promote the basic concepts of synthetic biology at the same time. Additionally, offline presentations are also a very effective method.

At the same time, when writing popular science articles, we also learned that the inflammatory mechanism of microplastics is mainly to cause inflammation. This also guided us to pay attention to its anti-inflammatory effect when modifying the Saccharomyces cerevisiae. In the subsequent circuit design, we hope to reduce the content of reactive oxygen species by introducing a series of enzymes such as SOD, in order to inhibit the inflammatory level in the intestinal tract.

Based on Dr. Fang's suggestions, we further created a science popularization video and a plasmid compilation manual. Additionally, our team members actively participated in summer social practice to promote our project and the basic concepts of synthetic biology.

Fig 16. Popularization through scientific communication

Fig 17. Summer practice activities for promoting synthetic biology

Fig 18. Group photo with Dr. Fang Xin

We have already formulated a preliminary route plan. However, when exploring the use of CRISPR technology to edit yeast genes, we encountered problems such as the spread of gene drives and metabolic toxicity caused by multi-gene introduction.

In order to clarify the safety risks of CRISPR technology in yeast gene editing and optimize the experimental design to ensure the safe application of the technology, we interviewed Professor Wang Yongming from Fudan University. We hope to obtain specific plans for risk prevention and experimental optimization from a professional perspective.

Screening single yeast clones and conducting sequencing can directly avoid the risk of CRISPR gene integration leakage; at the same time, simplifying gene construction and integrating some genes into the yeast genome can effectively reduce metabolic toxicity; moreover, through professional platform assessment, it is also possible to properly control the biological safety risks related to gene knock-in.

Professor Wang also raised the issue of metabolic toxicity, indicating that introducing too many genetic pathways would result in a certain metabolic burden. In response to the metabolic toxicity problem raised by Professor Wang, we further verified it through modeling.

Subsequently, we will screen the single yeast clones for sequencing to verify their safety, simplify the gene construction and attempt genome integration. At the same time, we will deepen the risk assessment and optimize the process by leveraging professional platforms.

The CRISPR technology can precisely edit yeast genes, providing an efficient tool for synthetic biology research. However, in application, there may be risks such as leakage and spread caused by specific gene integration, metabolic toxicity resulting from multiple gene introduction, and biological safety risks associated with gene knock-in. To address these issues, we plan to screen single yeast clones, sequence them, simplify gene construction and integrate some genes into the genome. Additionally, we will use professional platforms for assessment to reduce risks and ensure the safe application of the technology.

We have identified Saccharomyces cerevisiae as our chassis due to its well-characterized genetics, more complex post-translational modifications, and ease of genetic manipulation. However, we have encountered a new challenge—the risk of sporulation in Saccharomyces cerevisiae.

To prevent sporulation in Saccharomyces cerevisiae and ensure project safety, we consulted Professor Zhao Chunyan from the Department of Microbiology, seeking innovative insights for our project design.

Genetic engineering of Saccharomyces cerevisiae can be employed to disrupt sporulation pathways.

Based on this feedback, we plan to carry out our own experiments utilizing IME1-knockout strains of Saccharomyces cerevisiae to suppress sporulation and thereby safeguard project integrity.

Fig 21. An exclusive interview with Professor Zhao Chunyan, a microbiologist

Microplastics have become a pervasive environmental pollutant, detected in food, drinking water, and even the air we breathe. Long-term exposure to microplastics may pose potential health risks, including inflammatory responses and metabolic disturbances. Current solutions mainly focus on source control or post-consumption monitoring, but there is a lack of effective and safe methods to remove microplastics that have already entered the human body. Our project aims to address this gap by engineering a dual-strain system of yeast and lactic acid bacteria. The modified yeast is designed to adsorb microplastics in the gut, while the lactic acid bacteria assist in improving gut flora balance and product stability. Now, with the core design completed, we face the challenge of translating this biotechnology into a viable consumer product.

To ensure the product is both practical and acceptable to potential users, we set the following goals for the human practices phase:

(1) Safety Validation: Ensure the engineered strains are non-pathogenic and do not disrupt gut microbiota.

(2) User Experience Optimization: Develop a product form that is palatable, convenient, and accessible for daily use.

(3) Effectiveness Verification: Confirm that the product functions as intended under real-world conditions (e.g., pH and enzymatic challenges in the digestive tract).

(4) Public Perception Analysis: Understand potential users’ concerns regarding genetically modified organisms (GMOs) and microplastic-related health risks.

We interviewed gastroenterologists, nutritionists, and potential consumers (e.g., students, health-conscious individuals) to gather feedback. Key insights include:

(1) Safety: Doctors emphasized the need for rigorous biosafety testing, such as assessing strain colonization and potential horizontal gene transfer.

(2) Form Factor: Many suggested embedding the strains in familiar fermented foods like yogurt or probiotic drinks to enhance acceptability. Additional proposals included shelf-stable formats like freeze-dried powders or capsules for flexibility.

(3) Taste and Convenience: Consumers preferred mildly sweet or neutral flavors, with no gritty or artificial aftertaste. Single-dose, portable packaging (e.g., small bottles or sachets) was highlighted as ideal.

(4) Trust and Transparency: Non-experts expressed a need for clear labeling about GMO content, benefits, and scientific backing to build trust.

Fig 23. Word cloud chart related to public perception

Based on this feedback, we will take the following steps to refine our product strategy:

(1) Collaborate with food laboratories to test the viability of our strains in yogurt and fermented beverage matrices, optimizing fermentation conditions for maximum efficacy.

(2) Initiate small-scale sensory trials to evaluate taste and texture, iterating based on user preferences.

(3) Develop public-facing materials (e.g., infographics, FAQs) to transparently communicate the science behind the product and address GMO-related concerns.

(4) Plan pilot studies with volunteer groups to monitor microplastic reduction effects and physiological responses, ensuring the product meets both safety and performance targets before scaling.

Fig 24. Regarding the issue of product form, the closed-loop process

Our initial concept for the product is yogurt and fermented beverages, packaged with alginate. However, the implementation of food-related products requires considering numerous factors. Before further designing the product, we hope to listen to more professional opinions.

Incorporate more opinions to better design our products.

We introduced our project to Professor Qin Jun, a national-level talent. Professor Qin expressed a positive and affirmative attitude towards our project and also proposed different metabolic methods as solutions to the problem of microplastic accumulation. However, our initial conception of the yogurt product was opposed by Professor Qin. He suggested that when making the product, more attention should be paid to safety issues, and the metabolic form of the product in the human body should also be considered.

After our team's discussion and planning, we further improved the safety module to ensure the safety of our project both inside and outside the body. However, the design of the suicide gene and the concept of yogurt seemed to conflict - under the yogurt conditions, our host bacteria would trigger the expression of the suicide gene. Through brainstorming, we finally chose an alternative option and designed our product as freeze-dried bacterial powder.

Fig 25. Opinions from Professor Qin Jun

After we have determined the final product form, which is freeze-dried fungal powder encapsulated in microcapsules, we hope to obtain expert opinions to further improve the shortcomings of our project.

We hope to further refine our project by reviewing our timeline with the relevant researchers.

We interviewed Dr. Bao Yuheng, the liaison officer and coordinator of the Human Practice Committee of iGEM. Dr. Bao gave us a positive response regarding our human practice work. At the same time, he also pointed out that there were deficiencies in our project, namely a lack of understanding of the relevant policies for domestic food and health product production.

Our team members searched for relevant policies and bills and conducted a SWOT analysis on them.

Fig 26. The laws and policies related to our project

Fig 27.SWOT analysis of legal policies

After conducting an investigation, we have learned that the existing laws and regulations have to some extent restricted the implementation of our products. However, we still hope to promote the introduction of relevant laws and policies through the following measures.

Fig 28. future plan