Biologists digging into how bacteria break down a new generation of plant-based bioplastics have stumbled onto something unexpected: an enzyme that can dismantle both the plastic itself and a class of common antibiotics. The discovery, made by researchers at the University of Konstanz in Germany, raises questions about how the growing amount of plastic in soils and oceans might be reshaping the microbial world in ways that touch on antibiotic resistance.
The enzyme, named LCPH1, turned up during a study of long-chain aliphatic polyesters, or LCAP, a family of biodegradable plastics made from long molecular chains derived from plant oils rather than petroleum. Researchers buried strips of LCAP film in forest soil and later found it riddled with pits left by bacteria that had been feeding on its surface.
Lerner and his colleagues framed the work as a response to a problem that has outpaced easy fixes. “Plastic waste and its deterioration into micro- and nanoplastics, paired with slow biodegradation of most present-day plastic materials, has developed into a major environmental and human health concern,” the team wrote. Plastic debris does more than linger in soils and waterways, they added: it can also act as a vector that carries chemical contaminants and colonizing microbes from place to place, making the surface of a discarded plastic fragment its own small, mobile ecosystem.
Burying Bioplastic in a Forest Soil Experiment
Lead author Dr. Harry Lerner and colleagues buried the LCAP strips roughly ten centimeters deep in the upper humus layer of soil at the University of Konstanz’s botanical garden, then left them undisturbed for more than a year. That layer of soil is where cellulose and other natural polymers, including cutin, a plant-based polyester with a similar chemical backbone to LCAP, are normally broken down by resident microbes. Scanning electron microscope images of the recovered plastic later showed small, bacteria-shaped cavities pockmarking its surface, direct physical evidence that microorganisms had been colonizing and consuming the material over the course of the burial.
A ‘Pac-Man’ Shaped Enzyme With a Dual Appetite
To identify what was doing the eating, the researchers sequenced the DNA of the soil microbes living on the buried plastic. That search turned up LCPH1, a bacterial enzyme that closely resembled a class of proteins bacteria use to disable penicillin-type antibiotics. Structural modeling of the enzyme revealed an unusually wide, open active site that the researchers likened to a “pac-man” shape, spacious enough to grab onto both long plastic strands and much smaller antibiotic molecules. In laboratory tests, the enzyme not only broke the bioplastic down into its component parts but also destroyed penicillin and ampicillin, stripping both drugs of their ability to kill bacteria.
How LCPH1 Resembles an Antibiotic-Resistance Protein
“The enzyme’s 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,” Lerner said. Beta-lactamases are already a familiar problem in medicine, since bacteria that carry them can survive treatment with penicillin-family drugs. Finding an enzyme that straddles the line between a plastic-degrading esterase and an antibiotic-disabling beta-lactamase suggests the two functions may be more closely related, at a molecular level, than researchers had previously appreciated.
The Plastisphere as a Breeding Ground for Resistance
The discovery matters partly because of where it was made. Lerner and co-authors noted that plastic debris in the environment does not just persist as physical pollution; it also acts as a surface that microbes colonize, forming a biofilm community researchers call the plastisphere. Microorganisms inhabiting the plastisphere have been shown to carry disproportionately high levels of antibiotic resistance genes, the researchers wrote, raising concerns that plastic waste could help spread resistance genes through ecosystems as it breaks apart into smaller fragments and travels through soil and water. An enzyme that can act on both a plastic polymer and a beta-lactam antibiotic, in other words, sits at exactly the intersection researchers are most worried about: the point where the chemistry of plastic degradation and the chemistry of antibiotic resistance overlap.
Bacteria Adapting Faster Than Expected
Senior author Dr. David Schleheck, who has studied the plastisphere as a relatively new habitat, said the finding suggests microbes are adjusting to plastic in the environment more quickly than scientists had assumed. “Humans have only been introducing plastic into the environment in significant quantities for around 50 to 75 years,” Schleheck said, noting that in theory microbes would have had access to that carbon-rich material as a potential food source the whole time. “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,” he said. “I find this encouraging, because it seems that bacteria can adapt to breaking down polyester plastics more quickly than we expected.”
Designing Plastics Around What Microbes Can Break Down
Schleheck argued that the discovery points toward a practical strategy for tackling plastic pollution: designing plastics deliberately around chemical bonds that bacteria are already equipped to break. “To tackle the environmental problem of plastic pollution, we humans need to work with the capabilities of microbes,” he said. “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.” The findings were reported in The ISME Journal, with the full study, including the structural analysis of LCPH1, available in the peer-reviewed paper.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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