Study claims ‘water bear’ DNA is less foreign than previously thought

A study published in November rocked the scientific world when it concluded that tiny microscopic tardigrades have a genome that is comprised of 17 percent foreign DNA.

But now, a new study published in the Proceedings of the National Academy of Sciences journal has refuted that finding through an analysis that revealed tardigrades have 1 to 2 percent foreign DNA, at most.

Self-correcting science

Rather than disparage the previous report, Mark Blaxter, an author on the new study from the University of Edinburgh, cited modern science’s capacity to quickly self-correct.

“What would in decades past have taken many months to sort out became the focus of experts around the world and has been swiftly resolved. We hope this paper will finally correct the scientific record,” Blaxter said in a news release. “Tardigrades are amazing organisms, but these suggestions about their DNA were a step too far, even for their eight legs.”

Also known as water bears, tardigrades are exotic microorganisms that have the appearance of a bear-like creature straight out of a science fiction movie. The tiny creatures have become famous recently for enduring experiments that had them exposed to the extreme temperatures, radiation and other harsh conditions of outer space.

In the study published last year, researchers showed tardigardes had a significant chunk of their genome acquired through horizontal gene transfer, a process involving genetic transfer between organisms without reproduction. The process is quite common in microorganisms, but typically involved about 0.5 percent of organisms’ genetic material, not the 17 percent seen in the study.

The conclusion was considered revolutionary because it inferred that everything we know about evolution through genetic mutation could be wrong.

In the new study, researchers contrasted an independently acquired tardigrade genome to the one examined in the earlier published study. The scientists said they learned the tardigrade genome assembly made up of 17 percent foreign DNA was heavily affected by bacterial DNA and other contaminants. The authors made clear that contamination from foreign DNA is “easy to generate and difficult to separate.”

The new study ultimately found less than 1 percent of tardigrades’ genes are likely to have come from other species, an amount that is similar to our own genome.

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Image credit: Thinkstock

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