In the deep, dark Pacific, hydrothermal vents spew boiling-hot water and poisonous substances into the ocean. Hardly anything can survive in such a harsh environment. Yet somehow, one animal thrives.
Recently, scientists plunged into the depths of the west Pacific to explore these hydrothermal vents. As they discuss in their new paper, published in the journal PLOS Biology, the vents release not only boiling water, but also levels of hydrogen sulphide (a toxic gas) and arsenic (a potent carcinogen) that would be deadly to most animals.
Amazingly, they found an animal happily living in the hottest parts of these vents. It was Paralvinella hessleri, a species of worm.
“This was my first deep-sea expedition, and I was stunned by what I saw on the ROV monitor,” says Dr Hao Wang, lead author of the study, “the bright yellow Paralvinella hessleri worms were unlike anything I had ever seen, standing out vividly against the white biofilm and dark hydrothermal vent landscape.
“I could hardly believe that any animal could survive in such a dangerous place – just centimetres away from scalding hydrothermal fluids, surrounded by toxic sulphide gas.”
So how do the worms survive?
Using a remote-controlled vehicle with robotic arms, the researchers collected a few of the worms in order to study how they deal with such high levels of arsenic and hydrogen sulphide. Given that the worms are sessile (do not move around), the researchers could easily scoop them up with the vehicle’s robotic arms.
Back in the lab, the researchers found that the worms had so much arsenic in their bodies that it accounted for about 1% of their body weight. By analysing the worms at the cellular level, the scientists found that they use a surprising method to neutralise this arsenic, and it involves putting two poisons head-to-head.
As arsenic from the environment naturally accumulates in their skin cells, the worms absorb sulphide from the surrounding seawater. When sulphide meets arsenic, it forms a mineral called orpiment.
Orpiment is commonly found in volcanic areas. A dazzling yellow, it has been used by artists to create paint for millennia; there is even evidence that the ancient Egyptians used it in their artwork more than 5,000 years ago.
It is this vibrant mineral that makes the worms bright yellow.
While humans have developed a similar method to treat arsenic-contaminated water, we had no idea that animals might be using the same strategy. But how exactly the worms manage it at the molecular level is still unclear; more work needs to be done to understand the biological pathways involved in orpiment production.
“Understanding the underlying mechanisms could help us develop new approaches to dealing with environmental toxins,” Dr Wang says.
Top image: Paralvinella hessleri on hydrothermal vent. Credit: Wang H, et al., 2025, PLOS Biology, CC-BY 4.0
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