Scientists from the Max Planck Institute for Marine Microbiology in Bremen, Germany, have discovered that breaking down microbial bioplastics isn’t a skill reserved for microorganisms, like previously thought – but for a much wider range of animals. The findings were published in the journal Nature Ecology & Evolution.
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It all started with Olavius algarvensis, a species of marine worm that doesn’t have a mouth or gut but survives by digesting symbiotic bacteria that live beneath its skin.
This bacteria stores extra carbon and energy inside themselves as a substance called polyhydroxyalkanoate (PHA), which is essentially nature's version of plastic. Up until now, scientists assumed that only microorganisms could break down these biodegradable plastics.
“One of the worm’s bacterial symbionts stores enormous amounts of carbon as PHA,” said corresponding author of the research Nicole Dubilier, Director at the Max Planck Institute for Marine Microbiology. “We wondered whether the worm had evolved a way to access this rich energy reserve.”
So, they looked – and as it turns out, this unassuming worm produces an enzyme that can indeed break microbial PHAs into smaller molecules that can then be used for nutrition. The enzyme is produced right where the worm digests bacteria.
Even more surprisingly, this newly discovered skill isn’t unique to Olavius algarvensis – when the team examined different animal genomes, they found similar enzymes in over 66 species, including starfish, earthworms, sponges and a springtail.
“This was the real surprise,” said first author Caroline Zeidler, “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.”
Wider use
Bacteria make PHA naturally when they have more carbon than they need – later, when they need that carbon, they break the PHA back down and use it for energy.
In industrial bioplastic production, we’ve basically hijacked the 'making' part of this cycle. Companies grow PHA-producing bacteria in fermentation tanks, feed them sugars or plant oils, let them stock up on PHA, and then extract and purify it before it gets consumed.
PHAs are among the few naturally occurring, completely biodegradable plastics, and are widely utilised across different industries, such as medicine, packaging, agriculture and more.
The main advantage of these plastics is their biological circularity – microorganisms make them and can also later break them down. This is a sustainable alternative to conventional plastics, which don’t break down – microorganisms don’t recognise them as food, so they just physically separate into smaller and smaller pieces over hundreds of years, creating microplastics.
Interest in these bioplastics is growing and is expected to keep doing so in the coming years. According to the organisation European Bioplastics, current forecasts suggest that global biobased plastics production capacity will double from 2.31 million tonnes in 2025 to about 4.69 million tonnes by 2030.
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But currently, they still account for only a small share of the global market (roughly 0.5 per cent of the 431 million tonnes of plastics produced annually) because they’re often more expensive and complicated to manufacture.
The findings from Dubilier and her research team add a new player to this equation by showing that not only can other animals degrade natural bioplastics alongside microorganisms but also gain access to the carbon reserve and use it for nutrition.
“Our study changes our understanding of who can use these microbial carbon stores,” says co-author Maggie Sogin. “Animals have probably been feeding on nature’s original bioplastic for hundreds of millions of years – we’re only discovering it now.”
Read the full findings here.
Top image: Olavius algarvensis from Elba, Italy. Credit: Alexander Gruhl, CC BY-SA 4.0 via Wikimedia Commons
