In the ocean, plastic waste collects to form large garbage patches that endanger marine life. This is partly because the synthetic plastic polymers used today can only be broken down biologically, that is, by microorganisms, at a very slow rate. Instead, the physical fragmentation of these materials leads to the formation of microplastics and nanoplastics. However, microorganisms do colonize plastic waste in the environment, forming biofilms and creating a unique microbial habitat that researchers refer to as the ‘plastisphere’.
A research team at the University of Konstanz has now identified a new enzyme that can not only degrade certain polyesters and bioplastics, but also might provide bacteria with resistance to antibiotics. The discovery raises hopes that microorganisms can adapt to plastic degradation more rapidly than previously thought. Due to its structure featuring a wide-open active site, the researchers have named this ‘plastic-eating’ enzyme the ‘Pac‑Man enzyme’. Accelerating the environmental breakdown of plastic would require the use of biodegradable plastics wherever possible, as these materials can be decomposed by microorganisms.
The research project
In their research project, biologists Harry Lerner and David Schleheck from Konstanz investigated the complete microbial degradation of bioplastics. At the same time, they analyzed both the composition and the complete genetic makeup (the metagenome) of the microbial community involved in this degradation. For the study, the researchers used bioplastic materials – long-chain aliphatic polyesters (LCAP) – developed by chemist Stefan Mecking's team. Their joint study has now been published in the renowned scientific journal The ISME Journal .
How did the research team conduct their study? "We buried small pieces of LCAP bioplastic film in the upper humus layer in the forest at the university’s botanical garden, about ten centimetres deep", explains Harry Lerner. "This layer is where the breakdown of cellulose and other natural polymers, such as cutin – a plant-based polyester – takes place". In the laboratory, the team also mixed bioplastic powder into samples of the same forest soil. The forest samples were left untouched for a whole year, whilst in the laboratory, the CO 2 production – and thus the microbial respiration – was monitored in great detail over the course of one year too, in order to document the degradation of the materials. "Cellulose, other types of bioplastics such as PHBV and PCL, as well as high-density plastic (HDPE) and untreated soil were used as controls in the laboratory. We found that all bioplastic materials were completely degraded within roughly 250 to 330 days. Cellulose broke down after about 80 days, whereas virtually no degradation occurred for HDPE", says Lerner.
A surprising discovery
The analysis of the films retrieved from the forest soil held a surprise for the researchers: electron microscopy revealed tiny holes in the material, each of which matched the size and shape of a single bacterial cell. "We hypothesized that bacteria are coated with plastic-depolymerases anchored to their cell surfaces. This would enable them to digest their way into the material and become embedded within the film, leaving behind microscopic holes of exactly this type", explains Lerner.
In order to identify the microbes that accumulated in the soil samples during the degradation of the bioplastic materials, and the enzymes responsible for breaking them down, Harry Lerner extracted the entire DNA from the soil's microbial community, sequenced it, and analyzed the vast amount of data with great patience and care. The microbiologists identified a gene that was highly enriched exclusively in the forest soil containing LCAP. This gene encodes an esterase enzyme equipped with both a secretion signal, which directs the enzyme out of the cell, and a membrane-bound lipid anchor. This anchor ensures that the enzyme remains firmly attached to the bacterial cell surface. The ‘Pac-Man enzyme’ had been discovered.
The enzyme held yet another surprise. "Its structure resembles that of esterases, but also that of beta-lactamases, which are bacterial enzymes that are capable of cleaving the beta-lactam ring of certain antibiotics, such as penicillin, thereby making bacteria resistant to antibiotics", says Lerner. And indeed, the researchers were able to demonstrate the enzyme’s dual biochemical function – breaking down polyesters into monomers on the one hand, and cleaving penicillin on the other – in the laboratory.
A turning point in the plastisphere?
"The plastisphere is a new habitat in our environment," explains Schleheck. "Humans have only been introducing plastic into the environment in significant quantities for around 50 to 75 years. Since then, it has theoretically been available to microbial communities – such as bacteria, yeasts and fungi – as an additional source of carbon and energy for their growth. By 'theoretically', I mean that they would certainly like to use the plastic as a growth substrate – but they cannot, because the materials are actually indigestible to microbial metabolism and are therefore hardly degraded."
At least, so far. The ‘Pac-Man enzyme’ could signal a turning point, indicating that certain microorganisms may be able to specialize in breaking down plastic. "I find this encouraging, because it seems that bacteria can adapt to breaking down polyester plastics more quickly than we expected. To tackle the environmental problem of plastic pollution, we humans need to work with the capabilities of microbes. Ideally, this would involve using only polymers with biochemical breaking points, such as the hydrolysable ester bonds in polyesters like LCAP or other types of bioplastics", concludes Schleheck.
Key facts :
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Image 1 : https://www.uni-konstanz.de/fileadmin/pi/fileserver/2026/ein_enzym_das_hoffnung_macht_1.jpg
Caption : Electron microscopical images of an LCAP plastic film after a one-year incubation in forest soil, shown at increasing magnifications (a–d), as indicated by the scale bars. The images reveal micrometre-sized holes in the plastic film which are precisely the same size and shape as individual bacterial cells. The arrows in image c show the holes left by bacteria of different sizes, and the arrow in image d shows what is presumed to be a bacterial cell inside of one of these holes. The film was taken from dry forest soil in the summer of 2022, so it is likely that only a limited number of active microorganisms colonized it.
Copyright: The ISME Journal, DOI 10.1093/ismejo/wrag203, Figure 1
Image 2: https://www.uni-konstanz.de/fileadmin/pi/fileserver/2026/ein_enzym_das_hoffnung_macht_1.jpg
Caption : The image shows a structural model of the recently discovered plastic depolymerase, modelled using AlphaFold3. It has a particularly wide-open active centre to which large substrates, such as polymer chains, can bind. Models of the substrates bound to the active centre (modelled using AutoDock 4) are shown on the right for the bioplastics PCL and LCAP (PE-12,12), and for the beta-lactam antibiotic ampicillin. To the far left of the structural model is a flexible tail to which the membrane anchor (lipid anchor) can be attached.
Copyright: The ISME Journal, DOI 10.1093/ismejo/wrag203, Figure 7 cropped
The ISME Journal
Bacterial family-VIII esterase displays dual activities: hydrolysis of polyester bioplastics and β-lactam antibiotics
2-Sep-2026