Animals Can Digest Nature's Original Bioplastic

Plastic is usually discussed as something humans invented, but some microorganisms have been making natural plastic-like materials for an enormous span of evolutionary time. These compounds, called polyhydroxyalkanoates or PHAs, are stored inside microbial cells as reserves of carbon and energy. A study published on August 13 has revealed a surprising consumer of those reserves: animals. [1][2]

Researchers at the Max Planck Institute for Marine Microbiology began with Olavius algarvensis, a tiny gutless marine worm whose bacterial partners contain large amounts of PHA. The team found that the worm has an enzyme that can break down the material, allowing it to gain access to energy stored by its symbiotic bacteria. [1][2]

The researchers then searched more broadly. Related PHA-degrading enzymes appeared in more than 66 animal species across nine major animal groups, including starfish, sponges and terrestrial earthworms. Laboratory tests confirmed that enzymes from several distant animal lineages could degrade microbial PHAs. [1]

This changes an older assumption. Scientists had known that bacteria and fungi could break down these microbial storage compounds, but animals were not recognized as part of the process. The findings suggest that microbial PHAs may be a more direct food resource in ecosystems than previously understood. [1][3]

The discovery also attracts attention because PHAs are used industrially as biodegradable alternatives to some conventional plastics. However, the study does not show that earthworms or starfish can solve modern plastic pollution. It concerns naturally occurring microbial PHAs and the enzymes animals use to access them. [1][2]

The larger story is about food webs. A substance that looks like a technical material to humans can be an ancient energy reserve to microorganisms and, apparently, a nutrient source to some animals. The study adds a previously hidden route by which carbon can move from microbes into larger organisms.