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Tardigrades, already made of indestructible win, have shown upwardly once more in the scientific weirdness Hall of Fame this calendar week, thanks to a new study that sequenced the first tardigrade genome and found that 17.5% of it came from other species. Otherwise known every bit water bears, tardigrades are actually a large group of related species which have a key trait in common: They're impossible to kill. Tardigrades are the only species ever observed to survive outside Earth'south sheltering atmosphere. Now scientists are speculating that horizontal gene transfer, the phenomenon identified by a team of researchers at UNC every bit the reason for the unprecedented proportion of foreign Dna discovered in the tardigrade genome, may likewise be responsible for some of the tardigrade's famous immovability.

It's just a flesh wound!

Information technology'due south only a flesh wound!

If the thought of fully a sixth of an animal's genome being of foreign origin seems far-fetched, you're in expert company. Most organisms take a maximum of 1% foreign DNA. Creatures like Elysia chlorotica, which literally consumes a steady diet of other organisms to larn their powers (of photosynthesis), have been known to science for many years – until at present the rotifer, afar cousin to the h2o bear, was the most extreme example in its class for having acquired about 10% of its DNA from other species via horizontal gene transfer. Even the alarming miracle of increasing resistance to antibiotics has its roots in the fact that some single-celled organisms are very proficient at shaking down other microbes for their spare plasmids. But the proportion of foreign Dna in this clearly successfully adapted organism surprised even the researchers who did the experiment. Bob Goldstein, one of the co-authors of the study, said "We had no idea that an animal genome could exist composed of so much foreign Deoxyribonucleic acid. … We knew many animals acquire foreign genes, but we had no thought that it happens to this degree."

The method used to sequence the DNA in this experiment is crucial to the assertion that the Deoxyribonucleic acid constitute in the samples wasn't merely coincidental contagion by nucleic acid residue from other species. Traditional (Sanger) sequencing breaks DNA molecules into fragments, and then relies on further intervention to reassemble the fragments by matching up overlapping regions. In this study the researchers used a technique called single-molecule real-fourth dimension (SMRT) sequencing, created by Pacific Biosciences, which tin can process and sequence an entire DNA molecule without breaking it into fragments. Like having intact negatives to a photo, the intact molecule provides a master copy for comparing: The physical associations between genetic loci can exist used to parse out evolutionary history from the array of genes present in the living creature. Using this technique, the researchers were able to state with conviction that the genes had been acquired by the species inside its evolutionary timeline, and not introduced past experimental mistake.

Tardigrades

A light micrograph of a tardigrade. Credit: Sinclair Stammers

How did tardigrades get and then good at acquiring that much strange Dna? Thomas Boothby, atomic number 82 writer, believes it's related to the tardigrade's multifaceted arroyo to adversity. Nether dehydration stress, for case, h2o bears can really dry out themselves out, a process that breaks up their DNA into small pieces, much like the relatively stable form the genetic material takes during most of the cell's growth and replication cycle. When moisture returns, they rehydrate by making their cells leaky, which admits water – but also molecules from the environment, fifty-fifty macromolecules like DNA. And their robust DNA repair procedure is fault-tolerant enough to handle such tremendous disruption. That very fault tolerance may make the tardigrade more than likely to assimilate Deoxyribonucleic acid molecules from dissimilar species, since the ligation enzyme easily associates Deoxyribonucleic acid fragments with complementary glutinous ends.

Perhaps even more interesting is the fact that the squad discovered that under stressful conditions, their tardigrades could switch on and off some of that broad array of aftermarket genes – genes related, in their original hosts, to stress tolerance. It's vaguely reminiscent of that scene from Independence Solar day where Will Smith and Jeff Goldblum manage to hack an alien calculator with a MacBook, except this is real life and the hack actually works.

(Top photo credit: AMNH)