Scientists solve mystery of how earthworms digest toxins

While scientists have known that earthworms are capable of digesting fallen leaves and other types of plant material containing chemicals that are toxic to most other types of herbivores, how they were able to pull this off has long remained a mystery – until now, that is.

New research led by Dr. Jake Bundy and Dr. Manuel Liebeke of Imperial College London, published in Tuesday’s edition of the journal, Nature Communications, revealed that these worms have molecules in their guts to counteract the toxins produced by plants.

These molecules are called drilodefensins, and they are so highly abundant that there are at least one kilogram of them within the earthworms for every person on Earth – yet they are so precious that the worms recycle and reuse them. Dr. Bundy explained to redOrbit via email that they aren’t yet certain how these drilodefensins are produced.

“Normally, we would be able to search for earthworm genes related to relevant genes from other species. The problem here is that these drilodefensins aren’t like any other compounds, and so we know nothing about which genes are responsible,” he said. What he and his colleagues do know, thanks to their research, is how these molecules help with the digestive process.

Drilodefensin helps worms counteract plant polyphenols

Dr. Bundy explained that plants produce complex molecules known as polyphenols, used to alter the color and taste of coffee, chocolate, and wine. One of the primary reasons plants produce these compounds is as a chemical defense, and while the toxic compound isn’t targeted at earthworms, they can still affect worms after they fall to the ground.

“In order to be able to digest fallen leaves and other plant material, earthworms use their drilodefensin compounds as a protection mechanism,” the researcher told redOrbit. “They prevent polyphenols from binding and inactivating proteins in the earthworm gut. The drilodefensins do this because they are surfactants – that is, detergent-like molecules. (If you took a large amount of purified drilodefensins, you could use it to wash your dishes.)”

“As part of the study, we showed that even a regular commercial detergent (exactly the same compound that is often found in shampoo or laundry detergents) had the same protective effect against polyphenols, but were completely useless biologically as they also prevented the earthworm enzyme activity,” he added. “Presumably this is because the drilodefensins and earthworm enzymes have evolved together to be compatible.”

If the earthworms did not have these drilodefensins, they would not be able to eat and digest fallen leaves, thus returning the carbon locked inside dead plant material back into the ground, the authors said. The fallen leaves would build up, and the carbon cycle would be disrupted. They also found that the higher the polyphenol content that an earthworm’s diet is comprised of, the greater the amount of drilodefensins they produce.

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