At the beginning of 2024, as our team began exploring potential project directions, a World Water Report from the United Nations Environment Programme profoundly moved us. The report revealed that the global water crisis is deteriorating at an unprecedented rate. Annually, approximately 380-500 billion cubic meters of wastewater are generated worldwide, yet only 20% receives appropriate treatment before reuse. This severe reality prompted our team to contemplate deeply how synthetic biology could provide sustainable solutions to the increasingly critical water pollution crisis.

Among various types of wastewater, industrial wastewater presents the most challenging pollution source due to its complex composition and high toxicity. According to UN-Water data from August 2024, among 22 countries reporting industrial wastewater treatment status, only 38% of industrial wastewater was treated, and merely 27% was safely treated. Vast quantities of untreated or inadequately treated industrial wastewater are directly discharged into the environment, posing severe threats to ecosystems and human health.

Heavy metal pollution in industrial wastewater is particularly severe. Heavy metals cause persistent environmental damage due to their non-degradability, bioaccumulation, and high toxicity. As an iGEM team from Sichuan Province, we pay particular attention to local heavy metal pollution issues. The "14th Five-Year Plan" for Heavy Metal Pollution Prevention and Control in Sichuan Province explicitly identifies seven priority heavy metal pollutants: lead, mercury, cadmium, chromium, arsenic, thallium, and antimony. Among these, cadmium pollution has become a regional characteristic pollutant due to its widespread presence in Sichuan's mining and smelting industries.

Bioremediation technology, as an environmentally friendly treatment method, has attracted widespread attention in recent years. Particularly, engineered bacteria technology endows microorganisms with specific degradation or adsorption capabilities through genetic modification, demonstrating excellent treatment efficacy under laboratory conditions. However, our investigation revealed that these engineered bacteria, despite their superior laboratory performance, frequently encounter "loss" problems in actual wastewater treatment plant applications—microorganisms are flushed out of reactors by high-velocity water flow, unable to function stably. Resolving the immobilization problem of engineered bacteria to enable their stable operation in real industrial environments became the core challenge of our project.

Through systematic background investigation, we have clarified three key recognitions:

1. The tremendous potential of engineered bacteria technology forms a stark contrast with application bottlenecks. Engineered bacteria demonstrate obvious advantages in treatment efficiency, operating costs, and environmental friendliness, but microbial loss problems severely constrain their industrial application. Developing effective microbial immobilization technology becomes key to breaking through this bottleneck.
2. Regional pollution characteristics provide clear application scenarios for the project. Sichuan Province has listed cadmium as a priority-controlled heavy metal pollutant, and Chengdu faces cadmium pollution threats from upstream industrial activities. This provides realistic demand and application scenarios for developing biological treatment technologies targeting cadmium pollution.
3. The urgency of systematic technological innovation. Existing heavy metal treatment technologies each have limitations, urgently requiring the development of new treatment technologies integrating high efficiency, economy, and environmental friendliness. Combining the high efficiency of engineered bacteria with immobilization technology to construct a stable whole-cell immobilization platform represents a feasible path to solving this problem.

Based on these recognitions, our TasAnchor project was conceived. By engineering the biofilm protein TasA of Bacillus subtilis to enhance bacterial adhesion to polystyrene filter media, we construct a stable whole-cell immobilization platform. This innovation not only resolves the core problem of engineered bacteria loss but also provides an integrated solution for heavy metal detection, enrichment, and elution, contributing to the advancement of bioremediation technology toward industrial applications.