Artificial 'worm gut' used to break down plastics

By feeding worms with plastics and cultivating microbes found in their guts, researchers from Nanyang Technological University, Singapore (NTU Singapore) have demonstrated a nature-inspired method to accelerate plastic biodegradation and tackle the global plastic pollution problem. Their work has been published in the journal Environment International.

Previous studies have shown that Zophobas atratus worms — the larvae of the darkling beetle, commonly sold as pet food and known as ‘superworms’ for their nutritional value — can survive on a diet of plastic because their gut contains bacteria capable of breaking down common types of plastic. While their use in plastics processing has previously been impractical due to the slow rate of feeding and worm maintenance, NTU scientists overcame these challenges by isolating the worm’s gut bacteria and using them to do the job without the need for large-scale worm breeding.

“A single worm can only consume about a couple of milligrams of plastic in its lifetime, so imagine the number of worms that would be needed if we were to rely on them to process our plastic waste,” said Associate Professor Cao Bin. “Our method eliminates this need by removing the worm from the equation. We focus on boosting the useful microbes in the worm gut and building an artificial ‘worm gut’ that can efficiently break down plastics.”

To develop their method, the scientists fed three groups of superworms different plastic diets — high-density polyethylene (HDPE), polypropylene and polystyrene — over 30 days, while the control group was fed a diet of oatmeal. The scientists selected these plastics as they are among the most common in the world, with HDPE known for its high-impact resistance — making it difficult to break down.

After feeding the worms plastic, the scientists extracted the microbiomes from their gut and incubated them in flasks containing synthetic nutrients and different types of plastics, forming an artificial worm gut. Over six weeks, the microbiomes were left to grow in the flasks at room temperature.

The scientists found that compared to the control group, the flasks which contained the gut microbiomes from the plastic-fed worms showed a significant increase in plastic-degrading bacteria. Furthermore, the microbial communities colonising the plastics in the flasks were simpler and more tailored to the specific type of plastic than the microbes found on plastics that had been fed directly to the worms. When the microbial communities are simpler and targeted to a specific type of plastic, this translates to potential for more efficient plastic degradation when used in real-life applications.

“Our study represents the first reported successful attempt to develop plastic-associated bacterial communities from gut microbiomes of plastic-fed worms,” said first author Dr Liu Yinan. “Through exposing the gut microbiomes to specific conditions, we were able to boost the abundance of plastic-degrading bacteria present in our artificial worm gut, suggesting that our method is stable and replicable at scale.”

The researchers say their proof of concept lays the foundation for developing biotechnological approaches that use worms’ gut microbiomes to process plastic waste. They now want to understand how the bacteria in the superworm’s gut break down the plastics at the molecular level, which will help with engineering plastic-degrading bacterial communities in the future.

Image courtesy NTU Singapore.