Photo: Wang H, et al., 2025, PLOS Biology, CC-BY 4.0
The marine worm Paralvinella hessleri survives its extreme hydrothermal environment by binding two toxic substances intracellularly.
Deep-sea worm Paralvinella hessleri survives the high concentrations of arsenic and sulfide in its environment by combining them inside its cells into a less dangerous mineral, scientists report 26 August in PLOS Biology.
P. hessleri is, as far as is known, the only animal to inhabit the hottest parts of the western Pacific Ocean, where extremely hot, mineral-rich water vents from the seafloor. These deep-sea hydrothermal vents can contain large quantities of the toxic substances sulfide and arsenic. The deep-sea ecosystem is moreover unsuitable for photosynthesising phytoplankton and macroalgae – which are generally capable of converting the harmful form of arsenic into a harmless one. A research team from China discovered that P. hessleri not only tolerates this extremely hostile environment, but also stores exceptionally large amounts of toxic arsenic in its body: up to more than 1 per cent of its body weight, roughly ten times as much as in other comparable species.
Detoxification
To find out how the deep-sea worm tolerates conditions that are lethal to virtually all other life forms, the researchers collected worm specimens and water samples from two hydrothermal vents. Using advanced microscopy and DNA, protein and chemical analyses, they identified a previously unknown process: P. hessleri effectively fights poison with poison, detoxifying both substances simultaneously. The animal accumulates arsenic particles in its skin cells, where they probably react with sulfide that penetrates the skin from the surrounding water. This produces small granules of a golden-yellow mineral, orpiment, which is not entirely harmless in itself, but is markedly less toxic than free arsenic or sulfide. The orpiment granules are found in several parts of the body of P. hessleri that are in direct contact with seawater; not only in the cells of the outermost skin layer, but also in the epithelium of the oral tentacles and the gut. According to the researchers, the orpiment therefore serves no signalling function, despite giving the worms their characteristic bright yellow colour.
P. hessleri effectively fights poison with poison, detoxifying both substances simultaneously
Related worms living in other parts of the world, as well as certain gastropod species in the western Pacific known to accumulate arsenic, may employ the same strategy. The authors conclude: ‘We hope that this model will encourage scientists to reconsider the way in which marine invertebrates deal with toxic elements in their environment and potentially exploit them.’