At the confluence of nature and human beings, beaches, lakes and beaches are supposed to be picturesque places. However, these beauties are now obscured by plastic rubbish. These casually discarded plastic bottles, bags and food packaging not only destroy the harmonious beauty of nature, but also pose a great threat to the creatures in the water.

In 2017, mankind has produced 6.3 billion tons of plastic for the world, of which only 600 million tons have been recycled, 12% have been incinerated, and 79% have gone straight back to our ecosystem. Every second, more than 200 kilograms of plastic waste is discharged into the ocean. This rubbish has long been everywhere.

With the rapid development of industrialization and modern life, plastic products have gone deep into people's daily life. However, the extensive use and random disposal of plastics have led to an increasingly serious environmental problem: microplastic pollution. Microplastics, as a substance that is difficult to decompose, accumulate in the water body for a long time, causing direct damage to the organisms in it. Many aquatic organisms mistakenly ate these microplastic particles, which affected their growth and development. What is more serious is that these microplastics are enriched step by step in the food chain and may eventually return to the human dining table, bringing potential harm to human health.

In a survey conducted in 17 years, tap water from 14 countries on five continents was selected and 83% of it was found to contain microplastics.

In order to deal with this environmental crisis, human beings began to explore various ways to solve the problem of plastic pollution. Biotechnology, chemical technology and physical technology have all become the research direction.

1. Biodegradation-this method takes advantage of the natural abilities of microorganisms such as bacteria, fungi and algae to break down plastics into environmentally friendly substances such as biological macromolecules, carbon dioxide and water.

2. Chemical degradation-conversion of microplastics into smaller molecules, such as formaldehyde and benzene, by chemical reactions, such as the use of enzymes. But the disadvantage of this method is that the resulting substances may still be toxic.

3. Physical degradation-here, high-pressure water or ultrasonic shocks are used to break down microplastics into smaller fragments, but it only reduces the size of the problem, not really solves it.

4. Photocatalytic degradation-the use of specific photocatalysts to decompose microplastics by photoreaction. Although this method works for some plastic types, it is not a general solution. By mixing the photocatalyst into the plastic, the environment-friendly photodegradable plastic can be prepared, which has the desired effect in a certain service life, and after it exceeds the service life, or after it is abandoned far from the service life, it can decompose quickly and automatically under the condition of light. The automatic photodegradation of this polymer material usually requires a specific photocatalyst, which is degraded by photochemical reaction under the action of the catalyst.

Although the current efficiency of biodegradation is still low, it provides a sustainable and environmentally friendly way to deal with microplastic pollution. With the deepening of the research, we believe that we will find ways to improve its efficiency and really solve this global problem.

Introduction of gene circuit map and specific components

For the degradation of PET in the ocean, we have constructed the engineering bacteria, in which the engineering bacteria are divided into two systems, as shown in the figure, the left system is the degradation system, which mainly performs the function of degrading PET, and the right system is the anchoring system, which allows the engineering bacteria to anchor on the bacterial cellulose to prevent biological pollution.

we connect the PETase gene to the ice nucleoprotein gene, and the INP protein acts as an anchor protein to help PETase immobilize on the surface of E. coli. PETase is a known degradation enzyme of PET polymers, which has great potential for the degradation of microplastics. Japanese scientists isolated a new strain "EdeneLasaKayensis201-F6" from PET abandoned in landfills in 2016, which can completely hydrolyze an amorphous PET film at 30 ℃ in six weeks. These studies have shown the potential of microorganisms in PET hydrolysis. The ester bonds between the chains of PET polymers were destroyed by various hydrolases such as polyethylene terephthalate hydrolase (PETase), cutinase, lipase and esterase. PET was mainly separated into mono-2-hydroxyethyl terephthalic acid (MHET) and a small amount of bis-2-hydroxyethyl terephthalic acid (BHET), which was cleaved into EG and TPA by terephthalate mono-2-hydroxyethyl ester hydrolase (MHETase).

we modified E. coli so that it could express INP-CBD and anchored our E. coli to bacterial cellulose. Bacterial cellulose is a kind of polymer material with excellent biocompatibility and biodegradability, which can be used as a carrier to modify the attachment of Escherichia coli. Through bacterial cellulose binding protein, Escherichia coli can be effectively immobilized on the surface of bacterial cellulose, providing a stable biological reaction environment.We used the cellulose binding protein (BBa_K4380000)) characterized by the Lithuanian igem team (vilnius-lithuania) in 2022 as a binding protein for microbial immobilization techniques based on bacterial cellulose.

Both of our systems use INP and cell surface display technology. The basic principle of cell surface display technology includes anchoring the anchor protein (usually the cell surface protein) to the target protein, which is transported to the cell surface as a fusion cargo of the anchor protein. After the cell surface is displayed, because the enzyme is immobilized on the cell, the function and activity of the enzyme are maintained in the cell surface display system, which enhances its stability and reusability. In addition, the target enzyme is synthesized in microbial cells and then automatically transferred to the cell surface through the cell secretory system. This technology avoids the tedious and expensive process of enzyme separation and purification and has a broad application prospect. Cell surface display technology has been developed for biosensors for the detection of organic pollutants and whole-cell biocatalysts for the production of renewable biofuels.

With the combination of the two systems, the engineering Escherichia coli we constructed can display PETase protein on the surface of the fixed cellular cellulose carrier and play its role in the degradation of microplastics.

In the future water treatment system, the existence of our engineering bacteria can be used as a biological module to remove microplastics from the water in real time and make the water quality more pure. At the same time, our technology can also be applied to various environments polluted by microplastics to provide protection for our ecological environment.

To better adapt our project to deal with plastic pollution in the real world, we designed and manufactured a hardware device.

Application scenario：

1. Reservoirs and lakes: in order to protect freshwater ecosystems, such devices can be installed at the entrance of reservoirs or lakes to reduce microplastic pollution.

2. Fisheries: in farms or fishing areas, such devices can be used to purify the living environment of fish and other marine organisms and reduce their risk of ingesting microplastics.

Based on the design of this hardware device and our project, consumers can easily and safely degrade plastic pollution in an open environment.

Our project addresses the critical issue of microplastic pollution by harnessing the potential of biotechnology. We've engineered Escherichia coli to efficiently degrade microplastics in water, offering an innovative and eco-friendly solution. This development not only has economic benefits for industries affected by water quality but also promotes ecological sustainability, as our approach utilizes bacterial cellulose, a biodegradable biomaterial. Additionally, the platform we've created, combining bacterial cellulose with INP protein, holds promise for further applications in addressing various environmental pollution challenges, showcasing the immense potential of biotechnology in environmental protection.

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