South Africa’s ‘devil worm’ may offer heat-adaptation clues

9 Desember 2019

They call it the “devil worm,” but scientists studying the ability of a small nematode to survive environmental heat think its lessons on climate adaptation may turn out to be more providential than diabolical.

At the American University (AU) in Washington D.C., researchers who sequenced the devil-worm genome say it’s the first time it’s been done for any subterrestrial animal on the planet. The nematode was only discovered in 2008, when a surprised Gaetan Borgonie of the University of Ghent and Princeton University’s Tullis Onstott found it living in a South African gold mine at a depth of 1.3 kilometers underground.

Those scientists were studying microbes and didn’t expect to find the nematode in the aquifer, where the waters were carbon-dated to be 6,000 years old. Instead, they encountered this tiny organism surviving in extreme temperatures, and thriving in an environment with high methane levels and little oxygen. They quickly named it Halicephalobus mephisto in honor of Mephistopheles, the underground demon of German folklore famously celebrated in Johann Wolfgang von Goethe’s “Faust.”

Their initial discovery inspired other scientists – including NASA researchers – interested in the strange tale of the nematode and how it has adapted to its conditions. It’s what led AU scientist John Bracht and his team to sequence the H. mephisto genome looking for clues, with their findings published in November in the journal Nature Communications.

What they discovered is that H. mephisto had a remarkably high number of heat-shock proteins called Hsp70, which comparatively are absent in large numbers in other kinds of nematodes. Basically, these proteins help repair damage caused by heat stress. The scientists also found another gene “family” known as AIG1 in higher numbers, all leading to deeper research that suggests the genetic makeup of the nematode is linked to an evolutionary adaptation for its near-lethal climate.

“The Devil Worm can’t run away; it’s underground,” Bracht said. Based on the data, it’s most likely that seismic activity accounts for how a nematode existing in surface waters ended up in a deep subterranean home, rather than beginning as a native in the first place.

“It has no choice but to adapt or die,” he added. “We propose that when an animal cannot escape intense heat, it starts making additional copies of these two genes to survive.”

Part of that theory is based on work done by the research team to look for clues in other genome-sequenced organisms that carry a similar signature of increased Hsp70 combined with higher AIG1. The scientists found it in bivalves, the family of mollusks that includes clams, oysters and mussels, and conducted separate research on them. The bivalves also were heat-adapted, just like the devil worm, as are distantly related soil nematodes that have a high heat tolerance.

There is much more work to be done, but the scientists think they may have hit on an answer to how some organisms are adapting to warming temperatures, and that has implications for people and the planet. For example, the closest parasitic relative of H. mephisto is a deadly horse parasite that has killed humans too, and survived at high temperatures, but it has never been fully gene-sequenced.

“These genomic adaptive strategies are of significant concern to human and animal health, and as our climate warms, it will be increasingly important to understand their evolutionary dynamics,” the authors conclude.

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