Tardigrade, the only animal that can survive the extreme environment of outer space, has the highest percentage of foreign DNA and it swaps genes with other organisms
Researchers from University of North Carolina at Chapel Hill have sequenced the genome of tardigrade, a water-dwelling, eight-legged micro-animal, the only animal known to survive the tough conditions of outer space for the first time. And they found something weird about it.
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The huge part of its genome, nearly 17.5 percent, comprises of foreign DNA. This is the highest percentage of foreign DNA in any species.
Lead researcher Thomas Boothby and his team wanted to better understand how this tough animal was evolved and chose Hypsibius dujardini among the 700 species of tardigrade for assembling the genome from scratch. The outcome was full of genes which made researchers think that probably tardigrade’s own DNA was intermingled with other bacteria and organisms but soon they realized the results were genuine and the micro creature contains foreign DNA in high levels.
“We had no idea that an animal genome could be composed of so much foreign DNA,” said co-author Bob Goldstein from biology department in UNC’s College of Arts and Sciences. “We knew many animals acquire foreign genes, but we had no idea that it happens to this degree.”
Tardigrade is a nearly indestructible animal which can live anywhere from the top of the mountains to depths of oceans and can cope with the most inhospitable conditions with ease.
The findings raise several questions whether their ability to survive extreme conditions is linked to the weird DNA and also where does the DNA come from?
Researchers say the creature might have acquired genes from other microbes and bacteria through a process known as ‘horizontal gene transfers’ (HGT) in which genes can be swapped with each other. HGT is fairly common in bacteria but rarely occurs in animals and it points to the fact that the DNA was not inherited, it was traded.
"Animals that can survive extreme stresses may be particularly prone to acquiring foreign genes—and bacterial genes might be better able to withstand stresses than animal ones.” Boothby and his teams draw the conclusion from genome sequencing.
In order to survive the harshest of environments, tardigrades DNA breaks into pieces. The cell's membrane and nucleus, where the DNA resides, becomes temporarily leaky and DNA and other large molecules can pass through easily.
Tardigrades not only can repair their own damaged DNA as the cell rehydrates but also stitch in the foreign DNA in the process.
"We think of the tree of life, with genetic material passing vertically from mom and dad," said Boothby. "But with horizontal gene transfer becoming more widely accepted and more well known, at least in certain organisms, it is beginning to change the way we think about evolution and inheritance of genetic material and the stability of genomes. So instead of thinking of the tree of life, we can think about the web of life and genetic material crossing from branch to branch. So it's exciting. We are beginning to adjust our understanding of how evolution works."
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