Our story

Our school is based in Suzhou and most of our members are also from Suzhou. It is a city with great biodiversity. This means there are many different species and habitats that survive in Suzhou due to a lot of local lakes and rivers. Not only do our member comes from this beautiful city, but Suzhou is also the hometown of their family members. Which means there are lots of generations that have witnessed the changes in the environment in this city. Many members said that they heard the story from the older generation, and there are also many traditional stories about the wetland.

Specifically, one of the memorable stories that comes from our member Amelia’s grandmother, who greatly the wetlands have been affected. This is a true story that happened when her grandmother was young, and because Suzhou back then was still not a very developed city, most local citizens were farmers. Because of that, her grandmother would spend her off-school time helping her parents to plant the crops and her free time with her friends. In addition, the internet wasn’t even a thing back then. Because of that, the game that she played back then is all about things and creatures in the natural environment. The one of the games that kids back then would play was ‘finding the most amazing insect’, as seen in the name, this game requires people to find the most amazing insect that they think of within a limited amount of time, and show others about those insects. The winner would be the people who found the most interesting color and appearance of the insect. When we heard this story, all of us were shocked. Not only because we cannot play these games right now, but also because most of the land in Suzhou has already been converted into things like factories. But also, how wide biodiversity was back then, it’s only been around for around 60 years.

Another specific example which happens in our school is the dragonfly project that we took inside our school lab. In this project, member went to several lakes and the nearby wetlands in Suzhou to catch some dragonflies. After that, they would come back to school lab and sequence their DNA with the help from our biology teacher and categories them. During this project, one of the main outcomes is how genetic variation that we found of dragonflies lived in Suzhou. Even though our project was successful, we saw the damage that has been to these wetlands because of aggressive farming and heavy industrialization such as Electronics manufacturing, automobiles and garments Industry. Suzhou has aGDP of 267,270,000,000 yuan in total and apart from being an industrial hub it also has large swaths of agricultural land. All of this means that there has been massive habitat lost.

Therefore, from all these different stories that come from our members which were part of Suzhou citizens, we witnessed the changes and most specifically how the wetlands in Suzhou been destroy. Because of that, we decide to start this iGEM program.

Background

Heavy metal pollution has emerged as one of the most critical environmental issues of our time, largely driven by rapid industrialization and urbanization. Heavy metals and their toxic compounds are continually released into water bodies, the atmosphere, and soil as byproducts of various anthropogenic activities. Major contributors include mining operations, metal processing, paper manufacturing, and the synthesis of organic chemicals. These industries generate substantial quantities of heavy metal waste, which often enter the hydrosphere and lithosphere through landfill and waste dumping processes (Briffa, J 2020).

During the extraction, smelting, electroplating, and bleaching of metals, vast amounts of heavy metal-containing effluents are produced. Without effective management, these pollutants accumulate in the environment, eventually entering the biosphere and food web. This leads to unpredictable ecological impacts, such as changes in genetic diversity within affected populations. Although the relationship between heavy metal pollution and genetic diversity is complex, the genotoxic effects of these pollutants can increase mutation rates in exposed organisms, promoting the selection of tolerant genotypes and, in some cases, causing population bottlenecks or shifts in genetic composition (Tovar-Sánchez, E., 2018).s are particularly vulnerable to heavy metal pollution due to their position at the top of the food chain. Through the process of bioaccumulation, concentrations of heavy metals increase as they move up the food web. Many common vegetables—such as brinjals, gourds, spinach, tomatoes, and pumpkins—are known to absorb and accumulate heavy metals when grown in contaminated soils, especially near industrial areas. Long-term, unintentional intake of these metals poses serious health risks, causing stress and damage to the brain, muscles, nerves, and kidneys (Das, S., 2023).

Traditionally, the removal of heavy metals from contaminated water relies on physicochemical methods, the most common of which is chemical precipitation. In this process, chemicals (such as lime, sulfides, or other precipitants) are added to contaminated water to convert soluble heavy metal ions into insoluble compounds that can be separated from the water as sludge. While effective in reducing heavy metal concentrations, these methods are often associated with significant drawbacks. Chemical precipitation typically requires large amounts of energy for mixing, sedimentation, and sludge dewatering, leading to high operational costs. Moreover, the precipitants used can introduce secondary pollutants into the environment, and the resulting sludge may contain hazardous substances that complicate disposal and risk further contamination. Other conventional methods—such as ion exchange, membrane filtration, and adsorption on activated carbon—also tend to be energy-intensive, expensive, and may generate additional waste streams.

In addition to soil contamination, water heavy metal pollution has become a severe environmental challenge in China. Industrial discharges, mining effluents, and runoff from agricultural lands containing fertilizers and pesticides have led to the accumulation of toxic metals such as cadmium, lead, mercury, arsenic, and chromium in surface water and groundwater. Many major rivers and lakes, including the Yangtze, Yellow, and Pearl Rivers, have been found to contain heavy metal concentrations exceeding national quality standards. These pollutants not only threaten aquatic ecosystems but also pose significant risks to human health through drinking water and food chain contamination. The persistence and non-biodegradability of heavy metals mean they can accumulate over time, making remediation particularly difficult and urgent in order to safeguard both environmental and public health.

Given these challenges, there is a pressing need for innovative, sustainable, and cost-effective solutions to mediate heavy metal pollution. In particular, biological methods—such as the use of genetically engineered microorganisms or plants—hold great promise for addressing the limitations of traditional approaches by offering environmentally friendly and scalable alternatives.

Description

This year, our team is developing an innovative and sustainable biological platform for the mediation of heavy metal pollution using synthetic biology. We are focusing on creating solutions that are not only effective but also scalable and fits the sustainable development goal for real-world applications.

Therefore, we decided to engineer the cyanobacterium Synechocystis sp. PCC 6803 to efficiently capture, accumulate, and allow reduction of heavy metals such as cadmium, lead, zinc, and copper. To achieve this, we introduced genes encoding for both phytochelatin synthases (PCSs) and metallothioneins (MTs), under the control of a urea-inducible promoter for precise regulation. The engineered cyanobacteria will synthesize PCs and MTs in response to environmental cues, enhancing their ability to chelate and sequester heavy metals within the cell.

Our major functioning parts two remarkable classes of biomolecules: phytochelatins (PCs) and metallothioneins (MTs). Both play pivotal roles in nature’s strategy for heavy metal detoxification. Phytochelatins are small, cysteine-rich peptides primarily found in higher plants, fungi, and some algae. Their unique structure, composed of repeating γ-glutamylcysteine units followed by a glycine, enables them to chelate a group of essential heavy metals, including cadmium, copper, zinc, and mercury, in which, form toxic compounds in natural environment. The synthesis of PCs is catalyzed by phytochelatin synthase (PCS), a metal-activated enzyme. When cells encounter heavy metals, PCS rapidly converts glutathione—a common cellular antioxidant—into phytochelatins, which in turn bind and sequester metal ions, mitigating their toxicity and facilitating their compartmentalization within the cell. Notably, PCs not only detoxify metals but also help alleviating oxidative stress caused by metal-induced reactive oxygen species.

Metallothioneins, on the other hand, are small, cysteine-rich proteins found widely across bacteria, plants, fungi, and animals. Their high cysteine content enables them to coordinate and bind metal ions through metal-thiolate clusters. MTs are particularly important in the maintenance of the essential metals' homeostasis like zinc and copper, as well as in detoxifying non-essential and toxic metals such as cadmium and mercury. In addition to their metal-binding properties, MTs can also contribute to the scavenging of reactive oxygen and nitrogen species, providing further protection against heavy metal-induced cellular stress.

A major challenge in bioremediation is the recovery of the biomass after it has absorbed heavy metals. Traditionally, harvesting microalgae or cyanobacteria from water requires energy-intensive methods such as centrifugation, filtration, or chemical flocculants, all of which significantly increase operational costs and energy consumption. These conventional approaches can also introduce secondary pollution or leave chemical residues, undermining the sustainability of the entire process.

To overcome these limitations, our project introduces a self-aggregation strategy for the engineered cyanobacteria. Once the cells have accumulated heavy metals to saturation, we induce the expression of limonene, a hydrophobic terpene. The production of limonene increases the hydrophobicity of the cyanobacterial cell surface, promoting cell-to-cell adhesion and rapid self-aggregation. With this approach, the cells naturally clump together and settle out of suspension, making them much easier and more cost-effective to collect. By eliminating the need for expensive equipment or chemical additives, our self-aggregation system offers a greener, more efficient, and scalable solution for biomass recovery.

In parallel, we are also expressing PCS and MT genes in Moss Physcomitrella patens, a model species in synthetic biology. Mosses, with their unique resilience and adaptability, provide an exciting alternative chassis for heavy metal remediation. By comparing the performance of these proteins in both cyanobacteria and moss, we hope to identify the most effective system for different environmental conditions and applications, further expanding the synthetic biology toolkit for bioremediation.

Through this approach, we believe that our project can deliver a versatile and practical solution for the removal and recovery of heavy metals from polluted environments. Our work showcases the potential of synthetic biology to address critical environmental challenges with innovative, sustainable, and cost-effective technologies.

References

• Habjanič, J., Mathew, A., Eberl, L., & Freisinger, E. (2020). Deciphering the enigmatic function of Pseudomonas metallothioneins. Frontiers in microbiology, 11, 1709.
• Briffa, J., Sinagra, E., & Blundell, R. (2020). Heavy metal pollution in the environment and their toxicological effects on humans. Heliyon, 6(9).
• Hirata, K., Tsuji, N., & Miyamoto, K. (2005). Biosynthetic regulation of phytochelatins, heavy metal-binding peptides. Journal of bioscience and bioengineering, 100(6), 593-599.
• Mishra, S., Patel, A., Bhatt, P., Chen, S., & Srivastava, P. K. (2024). Perspective Evaluation of Synthetic Biology Approaches for Effective Mitigation of Heavy Metal Pollution. Reviews of Environmental Contamination and Toxicology, 262(1), 21.
• Tovar-Sánchez, E., Hernández-Plata, I., Martinez, M. S., Valencia-Cuevas, L., & Galante, P. M. (2018). Heavy metal pollution as a biodiversity threat. Heavy metals, 383.
• Das, S., Sultana, K. W., Ndhlala, A. R., Mondal, M., & Chandra, I. (2023). Heavy metal pollution in the environment and its impact on health: exploring green technology for remediation. Environmental health insights, 17, 11786302231201259.
• Shifaw, E. (2018). Review of heavy metals pollution in China in agricultural and urban soils. Journal of Health and Pollution, 8(18), 180607.