Background

With the escalating global plastic pollution induced by the exponential growth of plastic production, the inadequate disposal and absence of efficient recycling methods for plastic waste have resulted in severe environmental contamination.

Nevertheless, the current strategies for plastic waste management, such as landfilling and incineration, may exacerbate secondary pollution. One of the most difficult to deal with is polyethylene (PE)..Consequently, there is an urgent necessity to uncover a sustainable and convenient approach for the degradation of polyethylene (PE).We anticipate that employing biodegradation will render plastic degradation more environmentally friendly and cost-effective.

Problem

The current research on the biodegradation of polyethylene (PE) confronts several pivotal challenges:

Limited cultivability and identification of PE-degrading microorganisms: It is estimated that less than 1% of global microbial diversity can be cultivated using conventional methods. Research predominantly relies on isolating microorganisms from environments chronically exposed to PE and subsequently employing molecular biology techniques to postulate and validate key degradation enzyme genes. This reliance on inefficient traditional cultivation approaches severely restricts the scope for discovering novel, efficient enzymes from the environment. Consequently, while PE-degrading microorganisms are known to be widely distributed, the number of identifiable and practically applicable PE-degrading enzymes remains limited.

Inadequate understanding of the PE degradation process: Although PE-degrading microorganisms have been isolated from diverse environments, the precise mechanisms by which these microorganisms break down PE, the roles of key enzymes in this process, as well as the formation and microbial utilization pathways of intermediate products, remain unclear. This lack of comprehensive knowledge hampers the advancement of PE biodegradation strategies and technologies.

Method

In order to obtain and verify the gene sequence of an enzyme capable of efficiently degrading polyethylene, we conducted a thorough literature search and compared the identified gene sequences with our own sample's metagenomic database. We selected sequences showing a high degree of similarity as the target sequences.

Subsequently, we utilized bioinformatics tools to model the three-dimensional structure of the enzyme and performed molecular docking with hexadecane. The gene sequences of enzymes with strong binding affinity were selected for bacterial engineering and heterologous expression. Following bacterial expression, we lysed the bacterial solution to obtain the enzyme solution. The enzyme solution was then co-cultured with polyethylene film and polyethylene particles, and its weight loss rate was measured using a highly sensitive analytical balance after co-cultivation.

Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy were employed to analyze the surface morphology and functional groups of the polyethylene film and polyethylene particles post-co-cultivation. Based on these measurements, we assessed whether the enzyme exhibited polyethylene degradation activity.

Hope

Metagenomics provides us with a powerful new tool to fully mine the polyethylene degradation enzyme genes we want in environmental samples. Currently, we have found some coding sequences of polyethylene degradation enzymes through this technology and verified their effectiveness.

We believe that in the future, with this technology, we can find polyethylene degradation enzymes with faster degradation rates to solve the environmental problems we face. We have seen the great potential of this technology, and we look forward to its rapid transition from the laboratory to the market, so as to effectively solve the problem of white pollution.