Marine worms, starfish, and earthworms possess enzymes capable of breaking down natural polyhydroxyalkanoates, according to a study published in Nature Ecology & Evolution by researchers at the Max Planck Institute for Marine Microbiology in Bremen, Germany. This discovery overturns the long-standing scientific assumption that only microorganisms can degrade these natural bioplastics, revealing that animals exploit microbial carbon reserves across aquatic and terrestrial food webs.
How Animals Break Down Microbial Bioplastics
Microorganisms like bacteria and archaea produce natural bioplastics known as polyhydroxyalkanoates (PHAs) to store excess carbon and energy inside their cells. These compounds occur naturally in soils, sediments, and aquatic environments worldwide. Until recently, scientists believed that only microorganisms could dismantle these substances. Researchers found that a wide variety of animals possess the specific enzymes needed to break down microbial PHAs into smaller molecules.
The investigation began with Olavius algarvensis, an unusual marine worm lacking both a mouth and a gut. Instead of eating conventional food, the worm farms symbiotic bacteria beneath its skin and digests them. Corresponding author Nicole Dubilier, Director at the Max Planck Institute for Marine Microbiology, noted that one of the worm’s bacterial symbionts stores massive amounts of carbon as PHA. The research team discovered an enzyme within the worm that breaks down these microbial PHAs, and high-resolution imaging proved the enzyme is produced precisely where the worm digests its symbionts.
Did you know?
Animals may have been feeding on nature’s original bioplastic for hundreds of millions of years, according to co-corresponding author Maggie Sogin, formerly of the Max Planck Institute for Marine Microbiology and now Assistant Professor at the University of California, Merced.
Industrial Applications and Biological Circularity of PHAs
Beyond occurring naturally in the environment, PHAs are increasingly manufactured as sustainable alternatives to conventional plastics. Industrial production involves growing bacteria in large fermentation tanks supplied with carbon-rich substrates like sugars, starch, or plant oils. Under the right conditions, the bacteria accumulate PHAs, which are then extracted and processed into moldable, water-resistant materials.
These materials serve multiple everyday and specialized functions. PHA-based plastics are used in food packaging and hygiene products. In agriculture, fertilizers can be encapsulated in PHA beads that slowly release their contents as the plastic degrades. Medical applications include wound dressings, drug delivery systems, and resorbable implants or sutures that gradually break down in the body. Because they are produced biologically and degraded through natural processes, PHAs represent a closed loop of biological circularity, though they currently comprise only a small fraction of the broader bioplastics market.
Frequently Asked Questions
What are polyhydroxyalkanoates (PHAs)?
PHAs are natural bioplastics produced by bacteria and archaea to store excess carbon and energy inside their cells. They are fully biodegradable and serve as sustainable alternatives to conventional plastics.
Which animals can degrade natural bioplastics?
According to researchers at the Max Planck Institute for Marine Microbiology, animals ranging from marine worms and starfish to terrestrial species like earthworms possess enzymes capable of breaking down microbial PHAs.
How are PHA bioplastics used commercially?
Industrially produced PHAs are used in food packaging, hygiene products, agricultural fertilizer encapsulation, and medical devices such as resorbable sutures and drug delivery systems.
Next Steps in Carbon Cycling Research
The discovery that animals actively contribute to the breakdown of natural bioplastics changes how scientists understand carbon cycling in nature. Researchers emphasize that further study is required to determine how widespread this digestive process is across different ecosystems and how much it impacts carbon cycling. By studying unusual organisms like Olavius algarvensis, scientists continue to uncover unexpected biological interactions that redefine our understanding of microbial and animal interdependence.
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