Background
Microplastics, as new types of pollutants, have been widely distributed in marine and near-shore ecosystems, posing a serious threat to the ecological environment. Mangrove forests, as important ecological barriers, have a particularly prominent microplastic pollution problem.
Once microplastic enters the mangrove ecosystem, it may adsorb harmful substances such as heavy metals. When organisms accidentally ingest these microplastics, it will affect their digestive system and reproductive health, spread through the food chain and then disrupt the balance of the entire ecosystem, and even lead to the decline or extinction of some sensitive species. In addition, microplastics may also enter water bodies through rainfall and tidal action, further polluting water quality, affecting the living environment of aquatic organisms and posing a potential threat to human health.
Microplastics are prevalent in the top layer of mangrove soil at a depth of about 100 centimeters, and these plastic wastes account for about 70% of the total habitat pollutants. 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, PE & CO2 HUNTER, was thus born.
fig1. Mangroves
Project Design
This year, students from the Zhuhai Campus of Beijing Normal University (BNU) proposed the use of synthetic biology to deeply degrade microplastic PE in mangrove soils and to convert the CO2 produced in the process into organic matter to be remobilized back into the soil. The aim is to create an engineered bacterial system suitable for mangrove forests to be used for deep degradation of microplastics and to maintain their low carbon emissions.
Thus, PE & CO2 made its debut! We engineered two types of engineered bacteria. One, engineered Pseudomonas aeruginosa for deep degradation of microplastic PE in mangrove soils, we enhanced the ability of Microcystis aeruginosa to localize and aggregate polyethylene (PE) by designing fusion proteins that combine polyethylene-binding proteins and polyethylene-binding proteins with a PE-binding peptide and the alkane monooxygenase, AlkB. This innovative fusion proteins can be integrated into bacterial membranes to promote the adhesion of P. aeruginosa to the polyethylene surface, thereby accelerating the depolymerization process. Pseudomonas aeruginosa adhesion to the polyethylene surface, thereby accelerating the depolymerization process of P. aeruginosa. Secondly, the engineered Rhodopseudomonas palustris is used to absorb CO2 produced during degradation, and the introduction of Rubisco enzyme directed to evolve carbon fixation strengthens the connection of the whole engineered bacterial system through the biofilm electron transfer relationship between the two engineered bacteria, prompting the bicarbonate transporter to absorb the CO2 produced during the degradation of plastic.
We strongly believe that clean and effective bioremediation will be the focus of future research. We envision that this targeted approach could provide a promising solution for mangrove ecosystems to address plastic degradation and reduce carbon emissions.
Theoretical Basis
Bioelectrochemical Systems (BES)
Pseudomonas aeruginosa, a thriving microbe in bioelectrochemical systems (BES), produces versatile phenazine redox mediators. BES, especially microbial fuel cells (MFCs), are rapidly developing for renewable energy and bioremediation. MFCs generate electricity via extracellular electron transfer from microbes degrading organic matter.
Pseudomonas aeruginosa, a thriving microbe in bioelectrochemical systems (BES), produces versatile phenazine redox mediators. BES, especially microbial fuel cells (MFCs), are rapidly developing for renewable energy and bioremediation. MFCs generate electricity via extracellular electron transfer from microbes degrading organic matter.
Attempts to improve the biological efficiency of MFCs have therefore focused on understanding and improving these mechanisms. In mediated electron transfer, microorganisms utilize endogenous or exogenous soluble redox mediators that enable transmission of electrons to an external electron acceptor. In bacteria, endogenous secondary metabolites used as mediators include riboflavins in Shewanella, phenazines in Pseudomonas, and quinones in Lactococcus. These molecules undergo reversible oxidation and reduction and hence can be used repeatedly as electron shuttles.
In mixed microbial communities and biofilms, redox mediators may be shared among different species, potentially fostering syntrophic interactions. Naturally, microbial consortia are formed within these communities, characterized by complex interactions that often enhance resource utilization. Further research has revealed synergistic relationships involving both native redox mediators and non-redox mediator producers, with these effects being especially significant under oxygen-limited conditions. P. aeruginosa-derived redox mediators have been demonstrated to facilitate extracellular electron transfer in a synergistic interaction with other strains. This provides a good basis for the linkage design with Rhodopseudomonas palustris in the deep soil in our project.
So one of the key challenges in enhancing the performance of extracellular electron transfer(EET), particularly for the strain Pseudomonas aeruginosa PAO1, is improving the efficiency of microbial electron transfer to the anode and The number of microbial nanowires.
CBB Cycle in Rhodopseudomonas
In Rhodopseudomonas, the CBB cycle is central to their ability to photosynthesize under anaerobic conditions. These bacteria are able to use light energy to split water, release oxygen as a byproduct, and use the electrons and protons produced to reduce CO₂ into organic compounds.
The CBB cycle allows Rhodopseudomonas to thrive in environments that may be difficult for other organisms to survive in, such as deep mangrove soils with low oxygen levels or high concentrations of organic pollutants.
In addition, the ability of these bacteria to fix CO₂ and produce valuable organic compounds makes them important for biotechnological applications such as biofuel production and environmental remediation.
The CBB cycle of Pseudomonas aeruginosa is a complex and elegant biochemical pathway for fixing CO₂ and producing organic compounds. By harnessing the power of photosynthesis, these bacteria are able to thrive in a variety of environments and contribute to the global carbon cycle. In conjunction with the electron transfer system between RhodopseudomonasRhodopseudomonas and Pseudomonas aeruginosa, we rationalize the use of the CBB cycle to immobilize CO₂, which is inevitably produced during the degradation of plastics.
The CBB cycle allows Rhodopseudomonas to thrive in environments that may be difficult for other organisms to survive in, such as deep mangrove soils with low oxygen levels or high concentrations of organic pollutants.
fig2.The transfer process of Pseudomonas aeruginosa PAO1-Rhodopseudomonas palustris CGA009 electrons and carbon dioxide
