This project focuses on the health needs of lactose-intolerant individuals. Through biotechnological methods such as modifying probiotics to efficiently express lactase, we aim to develop safe and effective solutions. The ultimate goal of this project is to promote the application of synthetic biology in the field of public health. Safety is the core principle throughout the entire process. We have established a multi-dimensional protection system to cover all aspects as much as possible and ensure the safety of potential users and the environment.

We specifically designed and constructed the "Population Density Maintenance System" to ensure the safe application of engineered bacteria in the intestinal tract. This system relies on the core mechanism of "intestinal flora AI-2 concentration gradient → LuxS signal perception + ccdB response regulation → dynamic balance of flora density", which can precisely sense and autonomously regulate the density of intestinal flora: by perceiving the concentration of AI-2 signals produced by intestinal flora metabolism through LuxS protein (indirectly reflecting the total amount of flora), and then responding to the signal through the ccdB gene-mediated regulatory pathway, the proliferation rate of engineered bacteria is dynamically adjusted - avoiding excessive colonization of engineered bacteria that causes intestinal space imbalance, as well as preventing intestinal function disorders caused by the inhibition of natural beneficial flora, providing a core technical guarantee for the safe colonization, functional performance, and compatibility with the intestinal microecology of engineered bacteria.

In the scenario where the final system is successfully applied, its core advantage lies in achieving dual autonomous operation of "density self-regulation" and "function self-fulfillment": without relying on any external substances (such as exogenous inducers, nutritional supplements, etc.), the system can complete the regulation of bacterial density through its own signal perception-response mechanism, and simultaneously autonomously synthesize target functional molecules (such as lactase) to exert therapeutic effects. This "no exogenous intervention" automatic design ensures the system's independence and safety from an operational logic perspective, avoiding potential intestinal irritation and allergic risks posed by exogenous substances, and eliminating the interference of external intervention on the intestinal microecology or system functions, further enhancing the reliability and safety of engineered bacteria applications.

We ultimately selected Bifidobacterium longum ATCC 15707 as the core application strain, and its safety is fully supported by multiple authoritative certifications and taxonomic alignment. At the broader Bifidobacterium genus level, this group of bacteria is globally recognized as intestinal commensal beneficial microorganisms and has been included in official lists of safe microorganisms in numerous countries and regions. Moving to the specific subspecies classification, our target strain belongs to Bifidobacterium longum subsp. longum-a subspecies explicitly listed in China's Catalogue of Strains Allowed for Use in Food and Catalogue of Probiotic Strains Allowed for Use in Health Food. It is approved for application in the production of food and dietary

At the international authoritative certification level, the European Food Safety Authority (EFSA) has also included the genus Bifidobacterium in its "Qualified Presumption of Safety" (QPS) list. This further confirms the safety basis for application of this bacterial genus in food, dietary supplements, and other scenarios from a scientific evaluation standpoint.

Our laboratory safety consists of three parts: safety regulations, safety education, and daily management. During the project period, we received multiple safety trainings to ensure that each team member had mastered the basic experimental operations and was familiar with the laboratory regulations. Meanwhile, we have established a duty system and checklist to maintain our daily work.

All wet experiments were conducted in the laboratory established at the previous NENU-CHINA. In accordance with the regulations of the school and the Laboratory, all experimental procedures comply with the "General Principles of Laboratory Safety & Emergency Response Measures".

Before starting the wet experiment, the instructor and consultant provided detailed instructions on the correct use of laboratory equipment, emphasizing preventive measures when using dangerous equipment such as autoclaves. This kind of safety education enabled us to have a comprehensive understanding of the safety regulations that the laboratory should abide by and the safety precautions that should be taken during the experiment process.

Before the laboratory work officially began, we attached great importance to the construction of laboratory safety. Not only did we post the laboratory safety regulations and emergency handling guidelines in prominent places, but we also organized emergency evacuation drills including fire escape drills. In addition, we also provided a detailed explanation of the experimental safety handling to ensure that each member could master the necessary first aid knowledge and emergency response skills.

Laboratory duty management is an important component to ensure the smooth and safe operation of the laboratory on a daily basis. At present, the on-duty management of iGEM laboratories refers to the designation of on-duty personnel to be responsible for the daily maintenance, safety supervision and environmental cleaning of the laboratory, in order to ensure the cleanliness, safety and efficient operation of the laboratory environment. Our laboratory should formulate a duty roster, clearly defining the responsibilities and duty hours of each person on duty to ensure that there is a dedicated person in charge every day. Effective laboratory duty management can enhance the working efficiency of the laboratory, reduce safety risks, and provide researchers with a more comfortable and safe working environment.

In response to the key demands of safety control, we have additionally established a dual guarantee mechanism: On the one hand, we implement a "two-person collaborative duty" model to prevent issues such as untimely emergency response and omissions in safety inspections that may arise from single-person duty. The two can work together to complete "comprehensive inspections + key rechecks", further enhancing the accuracy of safety control. On the other hand, for some important instruments, dedicated usage precautions will be marked in advance in the duty log, and files will be shared in the group in a timely manner for double reminders to prevent accidents caused by the negligence of duty personnel.

Through this duty management plan, not only can the collaborative efficiency of the laboratory's daily operations be enhanced, but also a stable and orderly experimental environment can be provided for the research and development of iGEM projects. Through the safety control design of "double-person on-duty + key reminders", risks such as accidental storage of reagents, instrument malfunctions, and environmental hazards can be minimized to the greatest extent, creating an experimental working environment that is both safe and convenient for team members.

Finally, the project has consulted experts in fields such as biomedicine and pharmacy. For specific suggestions, please refer to the "Human Practice"section. We assess risks and formulate measures with a rigorous attitude, hoping to work together with the iGEM community to build a solid safety defense line through professional protection, so that technology can serve public health under controllable conditions. ​