Scientists Found Animals Have Been Eating Nature's Original Bioplastic

A marine worm barely two centimetres long has no mouth and no gut, and yet it just helped scientists overturn a decades-old assumption: that the biodegradable plastic microbes make can only be broken down by microbes themselves.

The Key Fact

KEY FACT
The team found related PHA-degrading enzymes in more than 66 animal species spanning nine different phyla, from sponges to earthworms.

Why This Matters

Many bacteria and archaea store carbon inside their cells as polyhydroxyalkanoates, a natural energy reserve. Until now, scientists assumed this carbon stayed locked inside the microbial world, with no direct route for animals to access it. The discovery breaks that assumption, suggesting animals may have been tapping into this enormous carbon reserve, found in soils, sediments and water worldwide, for hundreds of millions of years without anyone noticing. The finding carries practical weight too. PHA is increasingly manufactured as a biodegradable alternative to conventional plastic, used in food packaging, hygiene products, slow-release fertilizer coatings and dissolvable medical sutures, and researchers have separately been engineering enzymes to build PHA-related plastic components from methanol, which makes understanding how the natural material breaks down more than a matter of pure biology.

What Happened

The story began with an unusual marine worm called Olavius algarvensis, which lives buried beneath Mediterranean seagrass meadows. It has no mouth, no gut and no excretory organs. Instead, it farms symbiotic bacteria beneath its skin and digests them for food. One of those bacterial symbionts stores enormous amounts of carbon as PHA, which led researcher Nicole Dubilier, a director at the institute, and her team to ask whether the worm had evolved a way to tap that rich energy reserve. High-resolution imaging showed the worm produces an enzyme dedicated to breaking down the bioplastic, and that it manufactures this enzyme exactly where it digests its bacterial partners, indicating it can genuinely access their carbon stockpile.

How It Works

After that initial find, the team searched animal genomes broadly for similar enzymes and found them surprisingly often, in more than 66 species spanning nine different phyla. Laboratory tests then confirmed that enzymes taken from phylogenetically distant animals, including a sponge, an earthworm and a springtail, could also break down the microbial bioplastic in practice. "This was the real surprise," says Caroline Zeidler, the study's first author. "What started as a discovery in a single marine worm turned out to be a widespread capability shared by animals from very different branches of the tree of life."

What Happens Next

The researchers say the next step is establishing how widespread this process actually is in nature, and measuring how much it genuinely contributes to carbon cycling between microbes and animals. With global production of biodegradable bioplastics expected to grow substantially in coming years, the team believes understanding this natural PHA-degradation pathway could prove useful for an industry already trying to mimic a biological cycle that animals, it turns out, may have been part of all along.

Takeaway

The real finding here is not just that one strange worm eats bacterial molecules. It is that the capacity to digest this microbial carbon runs deep across the animal tree of life, from sponges to earthworms, and simply went unnoticed until someone thought to look.