Animals have been eating nature’s original bioplastic for millions of years

For millions of years, nature's original bioplastics have been consumed by animals, according to a recent discovery. Microorganisms had naturally produced these biodegradable plastics, known as polyhydroxyalkanoates (PHAs), and stored them as carbon and energy reserves inside their cells. Scientists had previously believed that only microorganisms could break down these PHAs.

However, new research from the Max Planck Institute for Marine Microbiology in Germany has revealed that various animals possess enzymes capable of degrading microbial PHAs. The study, published in Nature Ecology & Evolution, found that marine worms, starfish, earthworms, and other terrestrial species can utilize these natural PHAs.

The investigation began with the unusual marine worm Olavius algarvensis, which has no mouth or gut and relies on symbiotic bacteria living beneath its skin for nutrition. One of the worm's bacterial partners stores large amounts of carbon as PHA, leading researchers to wonder if the worm could access this energy reserve. It was found that a specific enzyme in the worm can break down microbial PHAs into smaller molecules that animals can utilize.

This enzyme is produced in the location where the worm digests its bacterial partners, allowing it to tap into the PHA reserves stored inside its symbiotic bacteria. The discovery was not limited to the marine worm alone, as related enzymes were also found in over 66 species across nine different phyla in animal genomes. Laboratory tests confirmed that enzymes from diverse animals, such as a sponge, an earthworm, and a springtail, could also degrade microbial PHAs.

This finding challenges the previous assumption that only microorganisms could break down these natural plastics and suggests that animals may play a significant role in the global cycling of carbon. PHAs are used in various industrial applications, including biodegradable plastics for food packaging, hygiene materials, fertilizers, medical devices, and more.

They are particularly notable for their biological circularity, as they are made by microorganisms and can be broken down through biological processes. The new findings indicate that animals have likely been consuming nature's original bioplastics for hundreds of millions of years, a discovery that was only recently uncovered. Scientists are now intrigued to learn how common this process is in natural ecosystems and its contribution to carbon cycling.