Tardigrades — also known as "water bears" — are microscopic animals that can live through almost anything: 30 years in a freezer, rapid dehydration, boiling and freezing temperatures, massive doses of radiation, baths in organic solvents, and a trip to open space. Today, scientists sequencing their genome have discovered clues to just how they do it — which may help us learn how to be just as tough ourselves.
Which may help us learn how to be just as tough ourselves
Over time, the species gained the ability to tolerate damaging effects of the kind of stresses the tardigrades regularly endure, according to the results published in the journal Nature Communications. Part of that involved losing bits of DNA that trigger cells to consume their own components and produce damaging hydrogen peroxide molecules in response to environmental stress.
But the tardigrade genome wasn’t just losing things that might harm them. They also gained protective genes and evolved new proteins that protect their delicate strands of DNA from breakage. When one of those proteins was introduced into a human kidney cell line, those kidney cells were able to withstand X-ray radiation and hydrogen peroxide significantly better than unmodified, normal cells.
There are nearly 1,000 species of tardigrades, which are usually less than one millimeter long, and have four pairs of legs that end in "claws and/or sucking disks." For today’s study, researchers from the University of Tokyo in Japan sequenced a particularly tough species. It’s not the first time a tardigrade’s had its genome sequenced, though.
The tardigrade genome has been a subject of intense debate, in fact. Last year, scientists from the University of North Carolina at Chapel Hill published the first whole tardigrade genome and concluded that a whopping 17 percent of their DNA was from other species, obtained in a process known as horizontal gene transfer. But soon after, a second paper contested those findings, arguing that in fact those microbial sections within the tardigrade genome were from contamination rather than a DNA swap meet.
A tardigrade crawls through moss. (Kunieda)
The tardigrades have "claws and/or sucking disks," after all
Today’s study is the third published tardigrade genome attempt — the first of a species that is especially good at surviving extreme conditions. The researchers managed to keep out contaminating microbes by disinfecting the eggs, starving the tardigrades, and treating them with antibiotics — a regimen only the hardy water bears were likely to withstand. The scientists calculated that only 1.2 percent of the tardigrade genome was from other, non-tardigrade species. Among that 1.2 percent were genes that help tardigrades neutralize molecules like hydrogen peroxide that are produced in response to stress, and can damage their cells. These new findings call into question the findings in the first paper and strengthens the position of the second.
The newly discovered proteins that make tardigrades so impervious to extreme conditions could one day enable us to harness that power — to create cells resistant to dehydration, or crops able to survive in space. But, perhaps even more importantly, they give us insight into creatures that will probably outlast us — and maybe even cockroaches — on this planet. The tardigrades have "claws and/or sucking disks," after all.