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Scientists sequence genome of devil worm, deepest-living animal

By
Brooks Hays
The microscopic devil worm, a species of nematode, was found living nearly a mile underground in an aquifer in South Africa. Photo by John Bracht/American University
The microscopic devil worm, a species of nematode, was found living nearly a mile underground in an aquifer in South Africa. Photo by John Bracht/American University

Nov. 22 (UPI) -- Researchers have sequenced the genome of the deepest-living animal, the devil worm, gaining new insights into the genetic adaptations required for life under harsh, subsurface conditions.

Scientists first discovered the devil worm, which they named Halicephalobus mephisto, in 2008, living in an aquifer nearly a mile underground in South Africa. The research team didn't originally set out to find an animal. Instead, scientists were sampling the subterrestrial bacterial communities that colonize active gold mines.

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Prior to the devil worm's discovery, scientists assumed only bacteria could survive such extreme subterranean environs: high temperatures, low oxygen levels and an abundance of methane.

Now, just more than a decade after its discovery, the devil worm has become the first extremophile animal to have its genome sequenced.

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"The genome of an extremophile animal is really interesting precisely because there are not many extremophile animals known," John Bracht, assistant professor of biology at American University, told UPI in an email. "Of those that are known, there are less that are amenable to culture in the laboratory so we can obtain sufficient biological material to do genomic studies."

According to Bracht, who led the genome sequencing project, most known extremophile animals are found in the deep sea. Retrieving genetic samples from animals living at the bottom of ocean trenches is too hard.

The sequencing work carried out by Bracht and his colleagues revealed several interesting genetic adaptations.

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First, scientists found the worm's Hsp70 gene, which produces Hsp70 proteins, is working overtime. Different forms of the Hsp70 gene are found in all life forms, and the proteins it produces promote healing in cells damaged by heat stress. The devil worm's genome codes for an especially large amount of heat-shock protein production.

Researchers also found extra copies of AIG1 genes, which studies suggest play an important role in boosting cellular survival in plants and animals.

The genetic adaptations found in the worm's genome are different than the kinds of changes observed in the genomes of simpler organisms, like extremophile bacteria.

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"Interestingly, the AIG1 genes we discovered are not even present in bacteria, as far as we can tell, and the precise family of Hsp70 expanded was also only found in more complex organisms," Bracht said. "So it's really critical to examine animals to understand how more complex life adapts to stressful conditions."

When researchers went looking for comparable genomes, they found clams, oysters and mussels boast similar combinations of expanded Hsp70 and AIG1 gene families. Like the devil worm, the bivalves have evolved to protect themselves against heat stress.

"The fact that the same two gene families are expanded, independently, in H. mephisto and bivalves -- clams, mussels, and oysters -- suggests a general method for adaptation to heat," Bracht said. "We expect to see this signature of expanded Hsp70 and AIG1 more and more as the planet warms."

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In addition to studying the effects of a warming planet on animal genomes, the latest findings -- published this week in the journal Nature Communications -- could aid the search for life on other planets.

"Because much of the search for extraterrestrial life focuses on the presence or absence of an atmosphere or suitable temperatures, H. mephisto teaches us that maybe underground life could survive in places we didn't expect before," Bracht said.

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