Overview

Since the 50s of the 20th century, the rapid growth of global plastic production, while driving the economy has caused serious white pollution, due to the current level of plastic production, the use of disposal methods, there is no effective way to recycle the waste plastics after use, the vast majority of plastics are piled up in the form of garbage in the natural environment, and polyethylene production accounts for about a quarter of the world's total plastic production, so it is urgent to find a green, economical and convenient polyethylene treatment method. Compared with the physical and chemical methods of degrading polyethylene, the method of degrading polyethylene by polyethylene degradation enzyme has the advantages of low energy consumption and high efficiency, but the number and types of PE degrading enzyme genes have been excavated from known cultivable microorganisms so far, and the generation of intermediate products and microbial utilization pathways when PE degrading enzymes degrading PE are still unknown. Therefore, the project uses metagenomics technology and bioinformatics methods to quickly and comprehensively mine microbial PE degradation enzyme genes, which provides more theoretical basis and practical evidence for the subsequent mining and screening of polyethylene degradation enzyme-related genes in the metagenome and the study of biological enzyme degradation of polyethylene.

At present, the recycling of polyethylene mainly uses physical landfill and incineration, which will bring secondary pollution to the environment. Landfilling solid plastic waste will lead to groundwater pollution, although the incineration of solid plastic waste will produce a lot of energy, but it will also emit toxic products, such as CO2, sulfur oxides (SOx) or dioxins and other persistent organic pollutants, thereby causing pollution to the atmosphere, the physical method is mainly mechanical recycling, the technology has higher quality requirements for the recycled solid plastic waste, and with the increase of the number of recycling, the performance of the reprocessed products will deteriorate. The chemical methods are generally molecular sieve catalytic degradation method, alkane cross metathesis method, ionic liquid degradation method, but these methods have the following disadvantages: although the hydrocarbon mixture produced by molecular sieve catalytic degradation method can be used as a source of fuel oil after separation and purification, it is accompanied by a large amount of energy consumption in the reaction process; The alkane cross metathesis method can react at medium temperature (150°C-200°C), but the reaction time is long and the catalyst is expensive. The ionic liquid degradation method also has problems such as long reaction time and unstable reaction. Molecular sieve catalytic degradation method, polyethylene-biomass co-degradation method and supercritical water degradation method, pyrolysis or chemical dissolution and other methods to obtain valuable petrochemical products, but in the recycling process requires high temperature, chemical reagents, H2 and other special conditions, which will lead to high production costs and safety requirements, which is not conducive to large-scale promotion. In contrast, biodegradation utilizes PE degradation enzymatic conversion that can be carried out under reaction conditions at lower temperatures and pressures, resulting in significantly lower energy and reagent consumption, and is also a harmless treatment strategy that produces no by-products during the degradation process. Traditional landfill, composting and incineration technologies are difficult to meet the protection requirements of the ecological environment, and biodegradation is an eco-friendly, low-cost and promising way to solve the problem of plastic pollution.

Now, the biggest obstacle facing biodegradation to solve the plastic problem is the biodegradation of PE. The related work of PE biodegradation mainly focuses on the screening of PE-degrading microorganisms by traditional selective culture methods, and then based on their transcriptomic information under the condition of a single carbon source, the relevant up-regulated genes are deduced through molecular biology methods, and the up-regulated genes are heterologously expressed to determine whether they have degradation function. This traditional selective culture severely limits the scope of searching for PE-degrading enzymes, which greatly limits the efficiency of traditional methods to mine novel enzyme genes.

In this experiment, the microbial gene sequences in environmental samples were analyzed by metagenomics technology, and bioinformatics analysis and quality assessment were used to analyze the gene expression and detect whether it has the function of degrading polyethylene by a variety of methods. In order to break through the limitations of traditional microbiological selective culture on the search for the range of plastic degrading enzymes, the coding sequences of polyethylene degrading enzymes with efficient PE degradation effects were more quickly and comprehensively excavated, and the theoretical basis and practical evidence were provided for the subsequent mining of PE degrading enzyme coding sequences.