Study Reveals Animals Can Degrade Microbial Plastics, Challenging Previous Assumptions
Groundbreaking research from the Max Planck Institute for Marine Microbiology in Bremen, Germany, has upended long-held beliefs that only microorganisms could decompose natural plastics known as polyhydroxyalkanoates (PHAs). Published in the journal Nature Ecology & Evolution, the study found that various animals—including marine worms, starfish, and earthworms—harbor enzymes capable of breaking down these biodegradable materials, indicating a new pathway for carbon from microbes to enter animal food webs.
A Unique Discovery in Marine Worms
The investigation centered on the marine worm Olavius algarvensis, notable for its lack of a mouth and gut. Instead, it relies on symbiotic bacteria beneath its skin as a nutritional source. “One of the worm’s bacterial symbionts stores enormous amounts of carbon as PHA,” explained Nicole Dubilier, the study’s corresponding author and Director at the Max Planck Institute. “We wondered whether the worm had evolved a way to access this rich energy reserve.”
Researchers confirmed this hypothesis by identifying an enzyme in the worm capable of breaking down microbial PHAs into smaller, usable molecules. High-resolution imaging demonstrated that this enzyme is produced in the same area where the worm digests its bacterial companions, allowing it to tap into the PHA reserves.
The findings extended beyond the single species. The research team discovered similar enzymes in over 66 different species across nine distinct phyla. Laboratory tests revealed that enzymes from distantly related species, including a sponge and a springtail, could also degrade microbial PHAs. “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,” remarked first author Caroline Zeidler.
Implications of Biodegradable Plastics
PHAs not only serve as energy and carbon reserves for microbes but are also utilized to create biodegradable plastics. In industrial settings, bacteria are cultivated in large fermentation tanks with carbon-rich substances, leading to significant accumulation of PHAs, which can be processed into plastic-like materials. The unique properties of PHA-based plastics, including moldability and resistance to water, have made them suitable for diverse applications, from food packaging to medical supplies.
While PHAs hold considerable promise due to their biodegradable nature, they currently represent a small fraction of the bioplastics market. Nevertheless, as interest in sustainable materials increases, the researchers anticipate growth in both demand and manufacturing capacity for bioplastics in the coming years.
Widespread Presence of Natural Bioplastics
Microbial PHAs are naturally occurring in various environments, including soils and aquatic ecosystems. They are produced when microorganisms have an excess of carbon, and their biodegradability sets them apart from many other types of plastic. The ongoing research highlights the importance of animal contributions to the breakdown of these bioplastics, suggesting a symbiotic relationship in carbon cycling that had previously gone unnoticed.
Co-corresponding author Maggie Sogin noted, “Our study changes our understanding of who can use these microbial carbon stores. Animals have probably been feeding on nature’s original bioplastic for hundreds of millions of years – we’re only discovering it now.”
Future Research Directions
Despite the significance of this new discovery, scientists are still exploring how prevalent this process is in natural ecosystems and its overall impact on global carbon cycling. This breakthrough invites further investigation into the complex interactions between microorganisms and animals, potentially unveiling biological processes that have remained hidden throughout evolutionary history.
