The key to breaking down plastic may be in caterpillars’ guts

MINNEAPOLIS — To destroy plastic, caterpillars go with their gut bacteria.

Caterpillars that nibble through polyethylene plastic cultivate a diverse community of digestive bacteria that process the plastic, researchers reported November 13 at the annual meeting of the Society of Environmental Toxicology and Chemistry North America. Dousing old plastic in a similar mix of bacteria might speed the breakdown of the persistent pollutant.

Polyethylene is widely used to make plastic bags and other packaging materials, but it hangs around in landfills for decades, perhaps even centuries. Recently, scientists identified several species of caterpillars that appear to eat and digest the plastic, breaking it down.  But dumping old shopping bags into a den of caterpillars isn’t really a practical large-scale strategy for getting rid of the plastic. So to figure out the insects’ secret, researchers fed polyethylene to the larvae of pantry moths, Plodia interpunctella, and then looked at the bacteria in the caterpillars’ guts.

Caterpillars that ate a control diet of bran and wheat had guts mostly dominated by Turicibacter, a group of bacteria commonly found in animals’ digestive tracts. But the caterpillars that munched on the plastic had a much more diverse native microbial community. In particular, they had high levels of a few types of bacteria: Tepidimonas, Pseudomonas, Rhizobiales and Methylobacteriaceae.

Some of these bacteria have been shown to colonize and help degrade plastics in the ocean, says study coauthor Anisha Navlekar of Texas Tech University in Lubbock, so it makes sense that the microorganisms also appear to be helping the caterpillars break down plastics.