A ‘Pac-Man’ enzyme eats some plastic. It eats penicillin too

Somewhere in a lab in southern Germany, a bacterium has been eating plastic with its mouth wide open.

That, roughly, is why researchers at the University of Konstanz nicknamed their discovery the “Pac-Man enzyme.” It’s a bacterial enzyme with an unusually wide active site, the business end where the chemistry happens, and it can digest certain polyesters and biodegradable plastics, ScienceDaily reported. The findings were published on Sept. 2 in The ISME Journal, according to the University of Konstanz announcement.

Then the researchers found out what else it eats. In lab tests, the same enzyme also broke down beta-lactam antibiotics, including penicillin G and ampicillin.

A mouth built for big meals

Most enzymes are picky eaters. They fit their target molecule like a key in a lock, and anything the wrong shape gets ignored. This one has a wider opening than usual, which lets it grab bigger and more varied molecules. Hence the arcade-game nickname: it’s less a key than a mouth.

That flexibility is what makes it interesting for plastic. Plastics are long, stubborn chains of molecules that most living things simply can’t break apart, which is why a bottle can sit in a landfill for centuries. An enzyme that can chew through some of those chains is a small crack in a very large problem.

What the soil test actually showed

Here’s the part that gets hyped and the part that gets skipped. In soil experiments, nearly all of the bioplastics tested were completely broken down within about a year, roughly 250 to 330 days, when left in soil samples containing the bacteria, Nature World News reported. Interesting Engineering led with the faster end of that range.

Conventional plastic, the kind in most packaging, remained largely unchanged, Nature World News reported.

Read that twice before you throw your recycling in the garden. This is not a bug that eats water bottles. It’s an enzyme that helps break down specific materials, mostly ones already designed to degrade, under lab and soil-sample conditions. As one report put it, none of the results show that a typical product labeled biodegradable will vanish in a backyard, a landfill or a roadside ditch.

The penicillin problem

The antibiotic finding is the plot twist, and it may turn out to matter more than the plastic.

Beta-lactams, the family that includes penicillin and ampicillin, are some of the most widely used antibiotics in the world. Bacteria that can break them down are, by definition, resistant to them. The researchers suggested the enzyme’s activity may be linked to antibiotic resistance, ScienceDaily reported.

That connects to a worry scientists already had about plastic pollution. Plastic waste creates its own microbial neighborhood, nicknamed the “plastisphere,” and research has found an unusually high prevalence of antibiotic-resistance genes there, Indian Defence Review reported. If the same enzymes that let bacteria feed on plastic also let them shrug off penicillin, plastic waste might be doing more than clogging oceans. It might be a training ground for drug-resistant microbes.

That’s still a hypothesis, not a finding. But it’s exactly the kind of connection that turns a quirky lab result into a public health question.

There’s a consumer lesson in here too. Products stamped “biodegradable” usually mean degradable under the right conditions, with the right microbes, over the right amount of time. This study shows how specific those conditions can be: one particular enzyme, specific materials, the better part of a year in microbe-rich soil.

Why this isn’t the cleanup miracle

Every few months, a headline promises that some bacterium or enzyme is about to solve plastic pollution. None of them have, and this one isn’t claiming to. It works on particular materials, it takes most of a year in soil, and it leaves conventional plastic mostly alone. The research also doesn’t mean the enzyme can consume every kind of plastic, as one report noted.

What it does offer is a better understanding of how nature might already be adapting to the waste we’ve dumped into it, and a candidate tool that engineers could one day tune. Enzymes discovered in the wild are often the starting point for industrial versions that work faster and on more materials.

The catch with the miracle

The cleanest summary is also the least satisfying: the Pac-Man enzyme shows that some bacteria can eat some plastics, slowly, and that the same trick may help them resist our medicine. It is fascinating, useful and a little unsettling all at once.

For years, people have hoped nature would evolve a way to clean up our plastic. It might be doing exactly that. The question this study raises is what else it’s evolving along the way.

Sources

• ScienceDaily: scientists discover a plastic-eating “Pac-Man” enzyme
• University of Konstanz via EurekAlert: new type of plastic-degrading enzyme discovered
• Nature World News: enzyme broke down bioplastics in about a year
• Interesting Engineering: “Pac-Man” enzyme breaks down bioplastics
• Indian Defence Review: enzyme that eats plastic and disables antibiotics

Photos

• “Petri Dish with Red Sample and Gloves” by imagesourcecurated, Envato Elements (featured image)