Mangroves are woody communities of plants growing in tropical, subtropical coastal intertidal zones or estuaries. They are considered as a special forest type adapted to land-sea transition zones and have the titles of "Coastal Guardian" , "Land Pioneer" and "Biodecontaminator" . As an important buffer zone between land and sea, mangroves have important ecological, economic and social functions and value. In the ecological function, mangrove forest has the effect of weakening wind waves.

Unfortunately, mangrove forests are facing a particularly prominent microplastic pollution problem. Due to its location at the border between the sea and land, mangroves accumulate a large amount of plastic waste brought by ocean currents. Today, MPs have been detected in different regions of mangrove ecosystems in several countries, including China.

Microplastics in mangroves absorb toxins, harming ingesting wildlife and disrupting ecosystems, potentially leading to species extinction. They also contaminate water, endangering aquatic life and human health.

While studying in the Guangdong-Hong Kong-Macao Greater Bay Area, where here is an area of 11,000 hectares of mangrove forest, making Guangdong province with the largest mangrove forest distribution area in China. We cannot sit idly by over the microplastic pollution of the local mangroves soil ecosystem.

In the Guangdong-Hong Kong-Macao Greater Bay Area, researches identified six microplastic polymers in mangrove sediments, with PE and PP being most prevalent. At the same time, PE is more difficult to degrade than other plastics such as PVC and PET, so we focus our research on PE microplastics with high content and difficult to degrade.

Pseudomonas aeruginosa PAO1 and Rhodopseudomonas palustris CGA009

Fortunately, mangrove soils are home to a wide variety of vigorous microorganisms that have the natural ability to break down plastic materials. Based on this finding, we selected Pseudomonas aeruginosa PAO1, a dominant species in mangrove forests, and genetically engineered it to enhance its ability to degrade plastics, in order to advance related research. In addition, we designed and modified another Rhodopseudomonas palustris CGA009 for degrading carbon dioxide produced after plastic, making the whole system more complete and harmless. This innovative project, Mangroves PE&CO₂ HUNTERS, was thus born.

Addressing the critical issue of microplastic pollution in mangrove ecosystems, we have embarked on an innovative project utilizing synthetic biology. Our goal is to develop a system that not only degrades polyethylene (PE) microplastics in mangrove soils but also converts the resulting carbon dioxide (CO₂) into organic matter, which can be reintegrated into the soil.

We introduce “Mangroves PE&CO₂ HUNTERS”, a project that has engineered two distinct bacterial species to tackle this environmental challenge. The first, P. aeruginosa, has been genetically modified to more effectively break down PE microplastics. We have designed a strategy that includes a PE-binding peptide and a PE-degrading enzyme, fused to create a passenger protein that enhances the bacteria's plastic-degrading capabilities.

To further enhance PE localization and aggregation, we have developed fusion proteins like AlkB2-Rd45-Adh and CYP-VHB. These proteins bind alkane monooxygenase to polyethylene-binding peptides, allowing P. aeruginosa to hydroxylate and process alkanes more efficiently while adapting to anaerobic environments, thereby accelerating the degradation of polyethylene plastics.

Furthermore, we have engineered R. palustris to sequester CO₂ produced during the plastic degradation process. This integration promotes a synergistic relationship between P. aeruginosa and R. palustris that facilitates CO₂ uptake and reduces the environmental impact of greenhouse gas emissions, while producing cellulose to enable carbon fixation.

Our project is designed with safety in mind, incorporating a suicide mechanism that activates once the engineered bacteria leave the mangrove environment, preventing any potential ecological disruption.

In summary, Mangroves PE&CO₂ HUNTERS represents a promising approach to mitigate plastic pollution and reduce CO₂ emissions in mangrove ecosystems, setting the stage for future research in clean and effective bioremediation.