The DNA of Halicephalobus mephisto, a tiny worm that lives deep underground, has been sequenced

Halicephalobus mephisto (Image courtesy John Bracht, American University)
Halicephalobus mephisto (Image courtesy John Bracht, American University)

An article published in the journal “Nature Communications” reports the DNA sequencing of a nematode nicknamed “Devil Worm” whose scientific name is Halicephalobus mephisto. A team of researchers led by Dr. John Bracht of the American University sequenced the DNA of this worm only half a millimeter long to try to understand the genetic reasons behind its ability to live even at over 3 kilometers deep underground in warm water veins, where there’s little oxygen and a large amount of methane. An article published in the “Journal of Molecular Evolution” reports the examination of some genes that this nematode has in common with some molluscs adapted to live in warm environments.

Halicephalobus mephisto was discovered in 2008 by Gaetan Borgonie and Tullis Onstott while they were investigating the underground bacteria communities in South Africa’s gold mines. In recent years this type of research is expanding to try to understand the natural processes underway in the subsoil and the ecosystems that inhabit it. The researchers expect to find multi-cellular life forms such as nematodes up to a few meters deep but the mines’ tunnels can go down to depths which only bacteria and archaea could be believed to inhabit. Consequently, the discovery of a multicellular organism at a depth of more than a kilometer represented a big surprise.

Gaetan Borgonie and Tullis Onstott carried out a follow-up research for a year to understand if the discovered nematode had been brought from the outside but the analysis of the water found in various veins gave results in their isotope dating that indicated an age between 3,000 and the 12,000 years. In essence, it’s an environment that remained isolated for millennia and the species of nematodes that was called Halicephalobus mephisto adapted to living in those conditions who knows how long ago. The discovery was reported in an article published in the journal “Nature” in June 2011.

The finding of specimens of Halicephalobus mephisto even at a depth of more than 3 kilometers, in conditions of very high pressure, with very little oxygen and in environments where there may be a lot of methane, inspired the name of the species and the nickname “Devil Worm”. To understand the genetic origins of those adaptations, Dr. John Bracht and his colleagues sequenced its genome and found some interesting genes.

A considerable number of Halicephalobus mephisto’s genes encode proteins of the HSP70 (Heat Shock Protein 70 kilodaltons) family, known because they’re widespread among all organisms to protect cells from various types of damage such as that caused by heat. Among the nematodes it’s also common to have genes that encode that type of protein but in no other species such an amount was found, in many cases copies of the same gene. This nematode also has several copies of the gene known as AIG1, also among those that protect cells but with mechanisms that are still poorly known in protecting against heat damage.

Those genes have also been found in many copies in bivalve mollusc species showing adaptations to warm environments. Dr. John Bracht, together with Megan Guerin and Deborah Weinstein, reported this discovery in the article published in “Journal of Molecular Evolution”. The hypothesis is that organisms that can’t escape from hot environments are forced to adapt or succumb. Mutants with multiple copies of the HSP70 and AIG1 genes survived and probably over time the copies increased.

These tiny worms may seem uninteresting but could provide important information on adaptations to extreme environments by multicellular organisms. These are research related to those on possible adaptations to climate change and to those of extraterrestrial life forms.

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