Scientists Discover 'Pac-Man Enzyme' That Degrades Plastic and Antibiotics

Buried ten centimeters deep in the forest soil of a botanical garden, small pieces of experimental plastic film sat undisturbed for a year. When researchers from the University of Konstanz retrieved them, they found something unexpected: the films were riddled with microscopic holes, each one precisely the size and shape of a single bacterial cell. This observation would lead to the discovery of an enzyme that offers a new angle on one of the planet's most intractable waste problems.

The ocean's garbage patches—vast accumulations of plastic debris—represent a crisis without obvious remedy. Synthetic polymers, the foundation of modern plastic production, resist biological breakdown almost entirely. Instead of decomposing, they fragment into smaller and smaller pieces, creating micro- and nanoplastics that poison ecosystems from the surface down. Yet within this waste, something unexpected has begun to happen. Bacteria colonize the plastic, forming biofilms in what scientists call the "plastosphere"—a new microbial habitat that exists nowhere else in nature, created entirely by human activity.

Harry Lerner and David Schleheck, biologists at the University of Konstanz, set out to understand how microorganisms might degrade bioplastics—engineered polymers designed to break down more readily than conventional plastic. They buried strips of a long-chain aliphatic polyester, or LCAP, in the humus layer of forest soil, the same zone where cellulose and other natural polymers naturally decompose. In the laboratory, they mixed powdered bioplastic into soil samples and tracked degradation over twelve months by measuring carbon dioxide production, a direct indicator of microbial respiration. The results were striking: the bioplastic materials broke down completely within 250 to 330 days. Cellulose, by contrast, degraded in roughly 80 days. Hard plastic—the conventional HDPE used in most consumer products—barely degraded at all.

The holes in the retrieved films suggested a mechanism. Lerner hypothesized that bacteria might be coating themselves with plastic-degrading enzymes anchored firmly to their cell surfaces, essentially eating their way into the material like microscopic tunnelers. To identify which microbes were responsible and which enzymes drove the process, the team extracted and sequenced the total DNA from their soil samples, then analyzed the genetic data with what Lerner describes as "great patience and care." They found a gene that had become highly enriched in the soil containing LCAP. It encoded an esterase enzyme—a protein capable of breaking chemical bonds—equipped with two crucial features: a secretion signal that directs it outside the cell, and a lipid anchor that locks it to the bacterial cell surface. The researchers named it the "Pac-Man enzyme" for its wide-open active site, the mouth-like cavity where chemical reactions occur.

But the enzyme revealed a second function that surprised even the researchers. Its structure resembled not only esterases but also beta-lactamases, a class of bacterial enzymes that cleave the beta-lactam ring found in antibiotics like penicillin, thereby conferring antibiotic resistance. In laboratory tests, the team confirmed that the same enzyme could both break down polyesters into their component monomers and deactivate penicillin. This dual capability suggests that bacteria in the plastosphere are evolving rapidly, adapting to exploit a food source that has existed for barely half a century.

David Schleheck frames the discovery as a potential turning point. For roughly fifty to seventy-five years, plastic has been accumulating in the environment faster than any microorganism evolved to consume it. Bacteria and fungi would theoretically prefer to use plastic as a carbon and energy source for growth, but the material proved indigestible—a locked door with no key. Now, some microorganisms appear to be developing the key. "That gives me personal hope," Schleheck says, "because it looks as though bacteria might be able to specialize in breaking down polyester plastics more quickly than expected." The implication is clear: if humans shift toward polymers with hydrolyzable ester bonds—the weak points that the Pac-Man enzyme exploits—microbial degradation could accelerate dramatically. The partnership between human chemistry and microbial metabolism might finally begin to close the loop on plastic waste. Yet the path from laboratory discovery to environmental remediation at scale remains uncertain, and the question of whether this enzyme can be deployed widely enough to meaningfully reduce the plastic already choking the oceans remains open.