Scientists have identified a plastic-degrading enzyme nicknamed the “Pac-Man enzyme” that could offer new insights into how bacteria break down certain bioplastics, raising hopes for improved strategies to manage persistent plastic waste.
Researchers at the University of Konstanz in Germany found that bacteria in forest soil could degrade nearly all the tested bioplastics within approximately 250 to 330 days under the experimental conditions. The findings highlight the potential role of naturally occurring microorganisms and their enzymes in breaking down plastic materials.
The research published in the journal The ISME Journal examined how bacteria interact with long chain aliphatic polyesters (LCAPs), a group of polymer materials that includes certain bioplastics.
How the ‘Pac-Man’ Enzyme Works
The study was led by David Schleheck, professor of microbial ecology and limnic microbiology at the University of Konstanz, and his postdoctoral research team.
Researchers investigated how microorganisms in forest soil break down plastic films. They mixed bioplastic powder into soil samples and monitored microbial activity for more than a year, measuring carbon dioxide production as an indicator of microbial respiration.
In a related experiment researchers buried small pieces of LCAP bioplastic film approximately 10 centimetres deep in the upper humus layer of a forested area at the university’s botanical garden.
When the plastic films were recovered, microscopic examinations revealed holes in their surfaces. The holes closely resembled the size and shape of individual bacterial cells, suggesting that bacteria were interacting directly with and penetrating the plastic material.
The researchers proposed that enzymes attached to bacterial cell surfaces help break down the polymers into smaller chemical units known as monomers and oligomers. These water-soluble compounds can then be absorbed by microorganisms and used to support their growth.
DNA Analysis Reveals a Plastic Degrading Enzyme
To identify the biological mechanisms behind the process, the research team analysed DNA extracted from soil samples with and without bioplastic material.
The analysis revealed abundant esterase enzymes in soil samples containing LCAPs. Researchers identified structural features suggesting that the enzyme could be transported outside bacterial cells and anchored near their surfaces.
This arrangement could allow the enzyme to act directly on plastic polymers breaking them into smaller molecules that bacteria can subsequently consume.
The researchers nicknamed the enzyme the “Pac-Man enzyme” because of its distinctive structure and activity. Structural investigations revealed wide open cavities that can accommodate large polymer molecules, helping explain how the enzyme may interact with plastic materials.
The discovery offers insight into the biological processes that enable certain microorganisms to use plastic derived compounds as a source of nutrients.
Could the Discovery Help Tackle Plastic Pollution?
Plastic waste remains a major environmental challenge because many conventional synthetic polymers degrade extremely slowly under natural conditions. Over time, discarded plastics can fragment into microplastics and nanoplastics, which can spread through water, soil and ecosystems.
Microorganisms, including bacteria yeasts and fungi, can colonise plastic surfaces and form communities known as biofilms. These communities, sometimes referred to as the “plastisphere,” are increasingly being studied for their role in the environmental fate of plastic waste.
Understanding the enzymes involved in polymer degradation could help researchers develop improved biological recycling methods or explore ways to accelerate the breakdown of suitable plastic materials.
However, the findings do not establish that the enzyme can eliminate all types of plastic waste. The experiments focused on particular polyester materials and specific soil conditions, and the degradation period varied with the material and experimental environment.
Although the findings are promising, additional research will be necessary to determine how effectively the enzyme works across different plastics, environmental conditions and larger scale applications.
Scientists will also need to establish whether the degradation process produces intermediate compounds that require further treatment and whether the enzyme can be adapted for industrial use.
The study nevertheless provides a valuable starting point for understanding how naturally occurring bacteria and their enzymes interact with certain bioplastics.
By uncovering the molecular mechanisms behind this process researchers hope to contribute to future technologies that support more sustainable plastic management and reduce the environmental burden of persistent waste.