We tend to think of “bioplastic” as a modern invention, something engineered in a lab to solve a very human problem. It turns out microbes got there first, by a few hundred million years.

Many bacteria and archaea produce natural biodegradable compounds called polyhydroxyalkanoates, or PHAs, storing them inside their cells as reserves of carbon and energy, nature’s own version of a pantry. Scientists have long assumed only microorganisms themselves had the enzymes needed to break these compounds back down. A new study from the Max Planck Institute for Marine Microbiology in Bremen just overturned that assumption.

The discovery started with an unusual creature: a two-centimeter marine worm called Olavius algarvensis that has no mouth and no gut. Instead, it survives entirely by farming bacteria beneath its skin and digesting them directly. One of those bacterial symbionts turned out to store an extraordinary amount of PHA, up to 42% of its cellular carbon. Researchers wondered whether the worm had evolved a way to tap into that reserve.

It had. The team identified an enzyme in the worm, a PHA depolymerase, that breaks the bioplastic down into molecules the worm can actually use, and found it was produced in exactly the spot where the worm digests its bacterial tenants.

Once they knew what to look for, the researchers found similar enzymes across a surprisingly wide range of animals, marine worms, starfish, and land-dwelling species like earthworms. That points to a previously invisible pathway: a way for carbon stored by microbes to move directly into animal food webs, something researchers had assumed simply wasn’t accessible to animals at all.

As co-author Maggie Sogin, now at UC Merced, put it: animals have probably been feeding on this natural bioplastic for hundreds of millions of years, we’re only discovering it now.

The finding has a practical edge, too. PHAs are increasingly manufactured as an eco-friendly alternative to conventional plastics, used in everything from food packaging to slow-release agricultural fertilizers. Understanding exactly how — and how fast — these materials break down in real ecosystems, animals included, matters for figuring out whether they really live up to their “biodegradable” promise in practice.

Original paper: Zeidler et al. (2026), Animal degradation of microbial storage polyhydroxyalkanoates, Nature Ecology & Evolution. DOI: 10.1038/s41559-026-03153-8