The larvae of a beetle species native to Central and South America can apparently survive with the plastic polystyrene as their only food source and even gain weight by ingesting it. This was the finding of a new study by the Australian University of Queensland, published in the journal Microbial Genomics. The researchers were able to demonstrate that the larvae of the species Zophobas morio (large black beetle), known as "superworms," are able to digest expanded polystyrene (EPS) thanks to the microbes in their intestines.
The Australian research team led by Chris Rinke of the University of Queensland fed the so-called "superworms" with expanded polystyrene – also known by the trade name Styropor – for three weeks. One control group received bran, another no food. The aim was to confirm the results of previous studies, according to which superworms raised exclusively on EPS survive. In addition, the researchers wanted to investigate how the intestinal microbiome of the superworms changed in response to EPS feeding. The researchers observed that the worms that received the EPS diet remained active throughout the duration of the experiment, although they moved more slowly than the worms in the bran group. The group that received no food moved the least. In the EPS group, there was a colour change in the excretion within 48 hours, and examination of the worms' digestive tracts revealed numerous EPS particles in the superworms' midgut and rectum. The particles were partially degraded and had microbial cells adhering to them. The researchers interpreted the results as evidence that the worms had begun to ingest EPS and, with the help of intestinal microbes, break it down, digest it and excrete it. They also found that the Styropor-fed worms not only survived, but had even gained some weight, showing that the worms could even obtain energy from the polystyrene. To evaluate the effects of the EPS diet on the worms' life cycle, the scientists also conducted a pupation experiment after the three-week feeding trial. They observed pupation rates of 92.9, 66.7, and 10.0 percent for the three groups of bran, EPS, and no feed, respectively. They also examined the intestinal microbiome of the superworms to identify microbes, metabolic pathways and enzymes that may be involved in the degradation of the EPS. The microbiome of the superworms in the EPS group differed from the bran group in several ways. The study showed a loss of microbial diversity, pathogens indicative of intestinal flora imbalance, and signs of a stress reaction. It could not conclusively clarify which parts of the microbiome are active in metabolising polystyrene and which genes are active during a EPS diet compared with normal feed. The ways in which the intestinal microbes degrade EPS to styrene also remained unclear.
Overall, Rinke says the results show that superworms can help reduce EPS litter. They could make a big contribution to recycling and sustainability research, he says. "Superworms are like mini-recyclers. They shred the Styropor with their mouths and feed it to the bacteria in their intestine." His research group now wants to identify the enzyme responsible for degrading the Styropor so that it can be further developed and used to break down plastic waste in recycling plants.