The Quest to Sequence the Genome of a Volcano-Dwelling Worm

Volcano-worm
This worm, Pontoscolex corethrurus, grows to a length of 4 inches and can incredibly withstand the stressors of living in soil abutting a volcano, with high temperatures, volcanic gases and low oxygen. Luis Cunha

On São Miguel Island, in the Azores archipelago in the middle of the North Atlantic, lives a curious Brazilian expat. Known as Pontoscolex corethrurus, this tropical worm cannot tolerate the isle's temperate climate. And yet it survives there in two areas: in artificially warmed pineapple greenhouses and the soil within an active volcano.

Finding P. corethrurus in greenhouses makes sense, as it is thought to have been transported here decades ago in crates of pineapples from Brazil, and the balmy earth in the greenhouses recreates conditions found in its native land. But Luís Cunha, a researcher at Cardiff University, was shocked to find the worms in large quantities in soil within the island's Furnas volcano, home to boiling hot springs and continuous gaseous emissions. The worms themselves are unremarkable, looking much like other earthworms, about 4 inches long and as thick as a pencil. But their new home is not: Here, the soil is hot, highly acidic, has little oxygen and a lot of carbon dioxide, and contains large quantities of normally toxic metalloids like arsenic. This would kill just about all known types of worms, Cunha says. And yet P. corethrurus seems to thrive. How does it do it?

One obvious difference is that those worms that live in the volcanic soils of Furnas have a thinner skin. While this might sound like a bad adaptation, it may actually allow them to more effectively use the small amounts of oxygen found in the soil, allowing the gas to more easily pass from the soil into the body, Cunha suggests.

But the real answer likely lies in the worms' genes. Cunha completed his doctoral thesis while at Azores University on the genetics of worms from pineapple plantations and those from within the caldera, and he found that some very strange things were going on with the genomes of the volcano dwellers.

First of all, many of the volcanic worms showed genetic evidence of self-reproduction, or parthenogenesis. This trait may allow the animals to grow their populations more quickly and reproduce in hostile areas where the normal environmental conditions for breeding—such as high levels of moisture and the absence of volcanic gases—aren't present, Cunha says.

The volcano dwellers also appeared to have a higher degree of nuclear variability, with more repetitive segments and base-pair rearrangements. It's unclear what role these changes might have. Finally, these worms also appear to have a significant degree of horizontal gene transfer, wherein chunks of DNA have been "borrowed" from other organisms like microbes, Cunhas says.

Azores-volcanoes
The volcanic landscape of Furnas, on São Miguel Island, where the worm P. corethrurus has adapted to live. Luis Cunha

All of these changes suggest that the volcanic worms could represent a newly evolved species. But how did these differences arise, and what role do they play in survival? To answer these questions, Cunha and colleagues plan to fully sequence the worm's genome. To do so, they are raising money on a website called Experiment, a platform for scientific fundraising, and they have only until the end of May to do so.

Completing the volcanic worm's genome will help Cunha's team understand how the animal has adapted to warmer-than-usual conditions. This, in turn, could help scientists better understand the genetic underpinning of adaptation to global warming, he adds.

"This project may give us answers to explain how it is possible for an animal to live in this extreme environment—high temperature, low oxygen, high carbon dioxide and high levels of heavy metals—and still function and reproduce, maintaining an apparently healthy population," says Maria do Carmo Barreto, a professor at Azores University.