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How Superworms Make Styrofoam Into a Healthy Meal

The dark beetle’s thick, glossy larvae, nicknamed “superworms,” ​​perhaps because of their size, are usually content to nibble on wheat bran. But several of the two-inch-long critters recently found themselves eating much weirder dishes in the service of science: polystyrene, the long-lived plastic packaging material sometimes known by the brand name Styrofoam.

What’s more, the larvae that managed to suffocate this peculiar raw material did not die, as you might expect. As scientists have documented in a paper published Thursday in the journal Microbial GenomicsIn fact, they gained a little weight and could turn into beetles most of the time, prompting the researchers to check their digestive systems for microbes that could break down the polystyrene. If scientists can understand the toolboxes of such microbes, they can come up with a better way to recycle this stubborn substance, which, if left alone, could persist in the environment for hundreds of years or more.

These aren’t the first insects to get polystyrene in a lab. Mealworms are known for: their ability to eat the substance that makes up peanut packaging, among other plastics, said Christian Rinke, a microbiologist at the University of Queensland in Australia and an author of the new paper. Both mealworms and superworms have been observed when consuming polystyreneand they lose this ability when they are given antibiotics. So researchers have concluded that their gut microbiome is probably behind this unusual talent.

The question was, what exactly was in those microbiomes? To find out, Dr. Rinke and his colleagues three groups of superworms in the lab. One group ate bran, the other ate polystyrene blocks, and the third ate nothing. (The experiments were temporarily halted due to the tendency of hungry superworms to become cannibals; giving each unfed superworm its own private space allowed the study to continue.)

While bran was clearly much more attractive to the superworms, they were willing to try polystyrene. Within 48 hours, the polystyrene group stools changed from light brown to white, and their weight crept up very slowly over the course of three weeks.

When the time came for the insects to turn into beetles, those who ate bran successfully completed the transition nearly 93 percent of the time; those who were starving only collected 10 percent. Strikingly, 66.7 percent of the polystyrene-eating larvae that were given the chance to pupate were successful. They managed to extract enough energy from the notoriously indigestible substance to transform.

“Polystyrene is definitely a bad diet,” said Dr. Rinke. But “the worms can survive — they don’t look sick or anything.”

The researchers determined all the DNA they could extract from the guts of the larvae. They were less interested in which specific microbes were present than in which enzymes were made as the microbes worked to break down polystyrene. They identified a handful of likely candidates — all types of enzymes known for their slicing and cutting abilities — that may have ripped polystyrene into smaller pieces.

“The next step will be to express those enzymes in the lab and verify experimentally that they do what we think they are,” said Dr. Rinke.

With more details about the conditions these enzymes require and the precise nature of their abilities, Dr. Rinke that one day an industrial process can be designed to recycle packaging foam. Currently, used polystyrene can be made into certain types of building materials to try and keep it off the landfill. A much better solution, however, would be a way to break down the components and then rebuild them into something new, perhaps using microbes that could spin them into fresh bioplastics.

“It would make the whole thing more interesting economically,” he said. “It would create something desirable.”

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