Five-centimetre long insect larvae called superworms can digest polystyrene: one of the most vexatious plastics.
The ability, according to new research, is in their gut bacteria: there are microbes in their guts that have plastic-digesting enzymes. These microbes could ultimately be used in processing and recycling plastic.
“Insect larvae have a history of being able to damage, or even eat holes in plastic,” says Dr Chris Rinke, a researcher at the University of Queensland’s School of Chemistry and Molecular Biosciences, and lead author on a paper describing the superworm’s microbiome genomics, published in Microbial genomics.
Rinke, and the rest of his team at UQ, wanted to understand the plastic-eating ability of darkling beetle (Zophobas morio) larvae. The larvae of this beetle are called “superworms”.
“There were a few reports out there – there was one about the waxworm, or common mealworm. And they are about 1-2cm. But the superworm is more than 5cm. It’s way larger. So that’s what we thought: maybe this guy can do it, too. And maybe even better, because it’s a bigger size. That’s how we got started.”
The researchers reared three groups of superworms, on either bran, polystyrene, or nothing, over a three-week period.
“We found the superworms fed a diet of just polystyrene not only survived, but even had marginal weight gains,” says Rinke.
“This suggests the worms can derive energy from the polystyrene, most likely with the help of their gut microbes.”
Superworms munching through polystyrene. Credit: University of Queensland.
The researchers then investigated the gut microbiomes of the superworms, using a technique called metagenomics.
“That allows us to recover all the DNA from those microbes in the gut. Then we can sequence that, and we can actually see which enzymes are encoded in there,” says Rinke.
“It’s a very powerful technique that allows us to explore the whole system.”
They detected several enzymes that could break down polystyrene in the superworms’ gut microbes.
More on plastic-digesting enzymes: Another round of microbes versus plastic
On its own, the bacteria is unlikely to degrade plastic – it needs some processing by the superworm first.
“Superworms are like mini recycling plants, shredding the polystyrene with their mouths and then feeding it to the bacteria in their gut,” says Rinke.
“The breakdown products from this reaction can then be used by other microbes to create high-value compounds such as bioplastics.”
The researchers are now investigating ways to grow the gut bacteria separately, and test its ability to break down polystyrene further.
“We can then look into how we can upscale this process to a level required for an entire recycling plant,” says co-author Jiarui Sun, a PhD candidate at UQ.
“It’s really early stages,” says Rinke. “But what we want to do next is get those enzymes and express them in the lab and characterise them in more detail so we know exactly under what conditions they work, what temperature, how efficient they are, and if one is more efficient than the other.”
What would a recycling plant based on these superworms look like?
“One could grow a large number of superworms, it is possible,” says Rinke.
“But it’s way more feasible to actually mimic what the worm does. So you’d have a mechanical grinding of the polystyrene. And then you’d have it in basically large Pyrexes, where you add the enzyme or multiple enzymes to degrade it. That’s how I envision it.”