Wednesday, November 25, 2015

ubiquitous indestructible cryptobiotic tards....,


theatlantic |  The toughest animals in the world aren't bulky elephants, or cold-tolerant penguins, or even the famously durable cockroach. Instead, the champions of durability are endearing microscopic creatures called tardigrades, or water bears.

They live everywhere, from the tallest mountains to the deepest oceans, and from hot springs to Antarctic ice. They can even tolerate New York. They cope with these inhospitable environments by transforming into a nigh-indestructible state. Their adorable shuffling gaits cease. Their eight legs curl inwards. Their rotund bodies shrivel up, expelling almost all of their water and becoming a dried barrel called a “tun.” Their metabolism dwindles to near-nothingness—they are practically dead. And in skirting the edge of death, they become incredibly hard to kill.

In the tun state, tardigrades don't need food or water. They can shrug off temperatures close to absolute zero and as high as 151 degrees Celsius. They can withstand the intense pressures of the deep ocean, doses of radiation that would kill other animals, and baths of toxic solvents. And they are, to date, the only animals that have been exposed to the naked vacuum of space and lived to tell the tale—or, at least, lay viable eggs. (Their only weakness, as a researcher once told me, is “vulnerability to mechanical damage;” in other words, you can squish ‘em.)

Scientists have known for centuries about the tardigrades’ ability to dry themselves out. But a new study suggests that this ability might have contributed to their superlative endurance in a strange and roundabout way. It makes them uniquely suited to absorbing foreign genes from bacteria and other organisms—genes that now pepper their genomes to a degree unheard of for animals.

Thomas Boothby from the University of North Carolina at Chapel Hill made this discovery after sequencing the first ever tardigrade genome, to better understand how they have evolved. Of the 700 species, his team focused on Hypsibius dujardini, one of the few tardigrades that’s easy to grow and breed in a lab.

At first, Boothby thought his team had done a poor job of assembling the tardigrade’s genome. The resulting data was full of genes that seemed to belong to bacteria and other organisms, not animals. “All of us thought that these were contaminants,” he says. Perhaps microbes had snuck into the samples and their DNA was intermingled with the tardigrade’s own.

But the team soon realized that these sequences are bona fide parts of the tardigrade’s genome.