Current situation: environmental pollution remains serious

Figure. 1 Slow cyanobacteria management in Lake Taihu.
Figure. 2: Casual discharge of domestic sewage
Figure. 3 High level of heavy metal pollution.

With the large amount of industrial sewage and human life wastewater discharge, heavy metal pollution of water has become a global environmental problem. Heavy metal pollution is not only a great threat to the ecological balance and the safety of drinking water, but also

can act together with other pollutants in living organisms, presenting a complex joint effect in the organism, and ultimately causing comprehensive toxicity. Take our country, China, as an example, there has been no breakthrough in the treatment of cyanobacteria in Lake Taihu, which meanly because that the environmental sewage treatment is costly, and some pollution sources are difficult to detect quickly.

At present, heavy metal detection methods mainly include inductively coupled plasma emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), and atomic fluorescence spectrometry (AFS), etc. However, these detection methods are not convenient enough to carry out effective treatment in a short term, especially the basic cost is high, which is not conducive to the use of large-scale or high-frequency. We can also use biosensor technology to carry out simple, rapid, sensitive and accurate in situ dynamic monitoring and analysis of important pollutants in the environment, which has shown great advantages and potential. However, biosensors are too demanding to be used in practical applications. Synthetic biology has reawakened the potential of whole-cell microbial sensors.

How to face it?

Using the idea of synthetic biology, we can connect the "genes" into a network, to improve microbial sensing to allow bacteria to monitor environmental pollution. That is to say, using the principle of computer work, bacteria work as hardware and genes work as software, to assemble an artificial new organism. The programmable "biological components" in the software of this organism are synthetic DNA fragments that can be connected at both ends, connecting the "biological components" directly to the DNA assembly in the cell. Once connected, each "biological component" will act like a computer. Once connected, each "biological component" is like a computer programme that has the ability to modify and control the cell. We can "command" the cell by putting in and combining different DNA fragments to make it produce different biological effects on environmental pollutants, so as to achieve the function of monitoring environmental pollutants. The similar application of luminescent bacteria in environmental pollution evaluation and monitoring was reported in the 1940s.

In response to the needs and challenges of environmental pollution, we joined the iGEM League, guided by the principles of "local people solving local problems", "tackling global challenges" and new purpose of environmental pollution. tackling global challenges" and new purpose of "most of all, do your part to make this a world that you want to live in". We focused on synthetic biology, and with the guidance of a professor and PhD from Southeast University, we carried out literature reading and discovered heavy metal aptamers that allow for specific heavy metal detection. For example, lead, mercury, cadmium, etc.; at the same time, most of these heavy metals can bind to the corresponding proteins, so we constructed plasmids containing reporter genes, which are able to express specific heavy metal-binding proteins for the adsorption of heavy metal pollutants in the aquatic environment. In order to be able to determine the presence of pollutants in the environment, we constructed heavy metal aptamers into expression vectors, in the presence of heavy metals, gene expression can be initiated, and at the same time express the reporter gene and the target gene, the fluorescent proteins can be detected intuitively, and the target proteins can be used for the adsorption of heavy metals, so as to make the management of environmental pollution possible.

Figure. 4 The switch plasmid detects heavy metals and expresses binding proteins.

How was it achieved?

To facilitate this goal, our project uses a filter paper-based cell-free expression system. The cell-free expression system is first prepared by freeze-drying the reagents and materials on filter paper so that the sample to be detected can be added dropwise to the filter paper for rapid detection. The freeze-dried paper-based biosensors are easy to store and transport, and provide a portable bioreaction platform.

Figure. 5 Biosensors based on paper-based cell-free expression systems


In Chinese traditional medicine, there are mutualisms, and there are also mutualisms in the ecological environment, there are antidote plants around poisonous snakes, and there must be microorganisms (bacteria) that can survive in the presence of heavy metals in heavy metal polluted environments, which are able to express the corresponding binding proteins, and thus can be used for heavy metal pollution control.


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