This Plastic-Eating Enzyme Can Do Something Else That Has Scientists Concerned

Harry Lerner and David Schleheck at the University of Konstanz set out to learn whether ordinary forest soil microbes could digest engineered biodegradable plastic. They came back with an enzyme that does the job and a complication nobody ordered. The enzyme, LCPH1, chews through long-chain polyester. It also breaks down penicillin G, almost completely, inside 24 hours in laboratory tests. Those two abilities sit in the same protein. One of them is a possible tool against plastic waste. The other touches one of medicine’s oldest problems. The team published the work in The ISME Journal, and the second finding is the reason other scientists are reading it closely.

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Breaking Plastic And Breaking Antibiotics Are The Same Trick

The overlap looks like coincidence and is not. Penicillin and ampicillin work because of a beta-lactam ring, a small four-sided chemical structure at the heart of the drug. Snap that ring open and the antibiotic stops killing bacteria. Bacteria that resist these drugs usually carry beta-lactamases, enzymes that do exactly that snapping. Polyester plastics are held together by ester bonds, which an enzyme breaks by adding water across them. Chemically, that is close enough to ring-opening that the same protein architecture can handle both jobs. When the Konstanz team looked at LCPH1’s structure, parts of it resembled beta-lactamases. Then they tested it against actual penicillin and it worked.

Scientists Buried Plastic to See What Would Happen

The experiment was deliberately unglamorous. Thin films of long-chain aliphatic polyester, abbreviated LCAP, went into the ground about four inches down at the university’s botanical garden in Konstanz. The soil there is full of microorganisms that spend their lives taking apart fallen leaves and wood, so the question was whether that existing machinery would recognize a synthetic polyester as food. In parallel, powdered bioplastics went into laboratory soil samples. There the team measured carbon dioxide coming off the samples, since microbes exhale it as they consume carbon. Rising carbon dioxide meant something was eating. The films stayed buried for months before anyone dug them up.

250 Days for Bioplastic, 80 for Cellulose, Nothing for Polyethylene

The laboratory numbers set the scale. Several biodegradable plastics broke down over roughly 250 to 330 days. Cellulose, the fiber that stiffens plant cell walls, went in about 80 days, which is what a material looks like when soil organisms have had millions of years of practice on it. Conventional high-density polyethylene barely changed at all. That is the plastic in milk jugs, detergent bottles, and most grocery bags, and its carbon-to-carbon backbone offers nothing for a hydrolase to grab. The gap between 80 days and effectively never is the whole story of why biodegradability depends on chemistry rather than good intentions.

Bacteria Appeared to Be Chewing Their Way In

When the buried films came out of the soil, the team put them under an electron microscope and found holes. The holes were small and their diameter roughly matched the size of a single bacterial cell, which pointed to a specific feeding behavior rather than general weathering. Most soil bacteria secrete digestive enzymes into their surroundings and absorb whatever dissolves. These appeared to be doing something different: keeping the enzymes fastened to their own outer surfaces and pressing directly against the plastic. The genetic sequence supported the idea, since LCPH1’s instructions include a feature for anchoring the protein to a bacterial cell surface. The holes were cells eating in place.

Why Researchers Started Calling It Pac-Man

Every enzyme has an active site, the pocket where it grips a molecule and cuts it. LCPH1’s is unusually wide and open. In structural images, the cleft resembles the arcade character’s open mouth closely enough that the nickname stuck. The shape is functional, not decorative. Polyester chains are long and bulky, and a narrow active site would never get a grip on one. A wide opening lets the enzyme take hold of a large chain and clip it into fragments small enough for a bacterium to absorb and burn for energy. That same roomy pocket is part of why it can also accept a penicillin molecule.

What the Antibiotic Tests Actually Showed

Two experiments carry the finding. In the first one, LCPH1 was given penicillin G, the original injectable penicillin still used against strep and syphilis. Within 24 hours, the drug was almost entirely broken down. In the second one, the team treated ampicillin with the enzyme and then checked whether the treated drug could still stop laboratory-grown bacteria from multiplying. It could not. The antibiotic had been chemically disarmed. Both results came from the enzyme working in isolation, under conditions the researchers controlled, which is a meaningful demonstration of what the protein can do and a separate question from what it does inside a living cell.

The Caveat the Researchers Put on Their Own Result

The tested enzyme was not the complete one. LCPH1 in nature is membrane-associated, anchored to the bacterial surface, and the team could not successfully produce that full version in laboratory bacteria. They worked instead with a shortened, soluble form that floats freely. That matters for interpretation. Whether the naturally occurring, surface-anchored enzyme protects a living bacterium from antibiotic treatment is unresolved, and the Konstanz researchers say so directly. A purified protein destroying a drug in a tube is not the same event as a bacterium surviving a dose. The honest statement is that the capability exists and its consequences in real environments have not been measured.

Plastic Debris Already Carries Its Own Microbial Ecosystem

Microbiologists use the term ‘plastisphere’ for the community of bacteria, fungi, and other microorganisms that colonize plastic surfaces in soil and water. Those organisms form biofilms, sticky layers where cells sit close together inside a shared matrix, and earlier studies have detected antibiotic-resistance genes within them. That is the context LCPH1 lands in. Biofilms are places where bacteria exchange genetic material efficiently, so a gene that confers two useful abilities at once has somewhere to spread. The open question the Konstanz work raises is how often an enzyme that handles both polyester and beta-lactam molecules turns up outside a laboratory, and nobody has surveyed that yet.

Some Buried Films Were Still Intact After a Year

The field results were less dramatic than the laboratory ones. Powdered bioplastic in controlled soil samples degraded on schedule, but films pulled from the botanical garden ground after a year were in places still visibly whole, carrying microscopic damage rather than disappearing. Outdoor soil is colder, drier, and less uniform than a laboratory flask, and the material was in sheets rather than powder. That gap is the practical takeaway. Biodegradable labeling does not mean a product vanishes if discarded outdoors. Schleheck has framed the goal as working with abilities microbes already have, which points toward designing plastics that soil organisms can reliably take apart rather than relying on disposal to sort itself out.