‘Superworms’ Eat–and Survive on–Polystyrene

'Superworms' Eat--and Survive on--Polystyrene thumbnail

One of the most distinctive things about Christian Rinke’s laboratory for microbiologist Christian Rinke is the loud crunching sound of wormlike larvae chewing through polystyrene and burrowing into plastic foam blocks. Rinke will first check for stragglers before he throws out a chewed through block. Rinke says that if the worm is still in there, he can hear it .”

Rinke and his colleagues have been feeding plastic to Zophobas morio beetle larvae–dubbed “superworms” for their large size–to see if the microbes and enzymes in their gut might offer insights into how to break down some of the staggering amount of plastic waste humans generate. These superworms can survive on only polystyrene. This plastic is used in many products including cups and packing peanuts. The worms are able to process plastic, which suggests that it is efficiently broken down in their digestive tract. Rinke, who is a researcher at the University of Queensland in Australia, said that worms are “basically like eating machines”. He co-authored a new study detailing his findings. It was published in Microbial Genoomics ..

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To investigate how superworms’ gut microbiome reacts to a purely plastic diet, the researchers split 135 of the creatures into three groups: one was fed only wheat bran, another was fed only soft polystyrene, and the third was given nothing. All worms were tested for cannibalism and the members of the starved groups were separated from each other. The bran-fed larvae were more healthy than their plastic-fed counterparts. They gained more than twice their weight in the three weeks that they were monitored. After this, some of each group’s worms were taken out and set aside to become beetles. Nine out of 10 bran-fed worms successfully grew into beetles and maintained the most diverse gut microbiome of all three groups. Plastic-fed larvae had less impressive growth, but they gained more weight than starved worms and two-thirds of them became beetles. Rinke states that polystyrene is not a good food choice for larvae. However, they seem to be able to extract some energy from the material.

This is likely due to a symbiotic relationship of a superworm with its gut bacteria. Rinke says that the worm basically shreds the plastic to allow bacteria to biodegrade it into smaller molecules. These smaller molecules may be easier to digest or could be used to make new plastic. The key to reproducing the polystyrene process on a large scale is knowing which bacterial enzymes the microbes in their gut use. The new study required sequencing the genomes from the worms’ intestines to identify those enzymes. Rinke states that metagenomics allows us to characterize all genes in the [digestive]. microbiome. Rinke says that previous studies of other insects weren’t as thorough, with only a few possible enzymes or bacteria in the gut.

Uwe Birthscheuer, head of biotechnology and enzyme catalysis at the University of Greifswald, Germany, has been eagerly awaiting these data since it became apparent that some insect larvae could eat difficult-to-degrade materials more than a decade back. This could help scientists to find a way to recycle them using biodegradation. Bornscheuer, who wasn’t involved in the paper but had been following the topic of research, says that the new work is “the first solid analysis where they looked at the metagenome.”

Polystyrene in the gut of a Zophobas morio beetle larvae
Polystyrene in the gut of a Z. morio beetle larva. Credit: The University of Queensland

Rinke identified enzymes that they believed were specifically designed to biodegrade the superworms’ gut polystyrene. Bornscheuer pointed out to the team, however, that the researchers could not break the strong bonds between carbon atoms within the plastic because of the order in which they had placed the enzymes. The researchers have now revised their steps based on this feedback. They will include the same enzymes later.

Rinke, his colleagues, are not suggesting superworms should go into landfills or polluted areas to eat plastic. However, their unique gut microbiome may be a key to a chemical process that can biodegrade the material. They have a lot of work ahead of them. They will use their metagenomic data from their new study to experimentally test what each bacterial enzyme does to plastic.

ABOUT THE AUTHOR(S)

    Fionna Samuels is a 2022 AAAS Mass Media Fellow at Scientifi

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