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Sunday, September 11, 2016

Tiny WATER BEARS Steal Dna From Other Species

    They are considered the toughest organisms on the planet and now scientists have discovered that the resilience of tiny water bears could be due to the fact they 'steal' DNA from other organisms.
   Almost a fifth of their genome comes from foreign organisms such as bacteria and plants, according to a new study.
   This patchwork of genes helps the tiny animals, also known as moss piglets or tardigrades, survive in the harshest of environments for years.

   Water bears live all over the world and are typically 0.020-inches (0.5 millimetres) long.

   They move very slowly and clumsily on their multitude of legs, but despite their unsteady gait, the creatures are highly adaptable and can survive extreme temperatures.

   Even after being stuck in a freezer at -80 ºC (-112ºF) -112 degrees for 10 years, they can start moving around again 20 minutes after thawing.

   By sequencing these creatures' genome, researchers from the University of North Carolina (UNC) at Chapel Hill were surprised to find that 17.5 per cent - nearly a fifth - of the genome came from foreign organisms.

   For most animals, less than one per cent of their genome comes from foreign DNA.

   Another microscopic animal, the rotifer, previously held the record with eight per cent of its genome coming from foreign DNA.

We had no idea that an animal genome could be composed of so much foreign DNA,' said co-author Bob Goldstein of 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.'

   The study, published in the journal Proceedings of the National Academy of Sciences (PNAS) also made unusual findings about how DNA is inherited.

   The team found that water bears obtain around 6,000 foreign genes mostly from bacteria, as well as plants, fungi and Archaea single-cell organisms.

  '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,' said first author Thomas Boothby, a postdoctoral fellow in Dr Goldstein's lab.

   Indeed, bacteria have survived the most extreme environments on Earth for billions of years.

   Water bears acquire foreign genes through horizontal gene transfer, a process by which species swap genetic material instead of inheriting DNA from parents.

  '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,' Boothby said.

   Researchers said the DNA likely get inside the genome 'randomly', but what remains allows water bears to survive in the most hostile environments.

   Under intense stress, such as extreme dryness, the water bear's DNA breaks up into small pieces, the research team explained.

   Once the cell rehydrates, its membrane and nucleus housing the DNA temporarily becomes leaky and allows other large molecules to pass through easily. 
   They thus repair their own damaged DNA while also absorbing foreign DNA as the cell rehydrates, forming a patchwork of genes from different species.

  '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,' Boothby explained.

  'It's exciting. We are beginning to adjust our understanding of how evolution works.'

   In July 2014, a new species of water bear was discovered living in Antarctica - and it's so tough it can survive in space.

Scientists found the creature on a trip to Victoria Land some 3,500 miles (5,600km) south of Australia.

   A number of them, no bigger than half a millimeter, were lurking on mosses within a crater hollowed out by ancient glaciers.

   Members of the tardigrade family have been found in high mountains, hot deserts and the deep ocean - but never in Antarctica.

   And they're so resilient to harsh environments they've even been exposed in space by astronauts - and remarkably survived the experience.

   The water bear is the only kind of creature known that can survive in the vacuum of space.

   Dr Sandra McInnes of the British Antarctic Survey, who helped verify the find, said: 'Under the microscope they are slow walkers but they look like bears walking.

  'They have four pairs of legs but they can hold their back tow legs down and arch themselves up to reach things.

  'The cone-shaped mouth has a little hole in the middle for food and it has two eyes which can sense light too.

  'Their muscles help them manipulate their claws like a human hand being opened and drawn back in again and they look rather like an armadillo.

  'But if you can imagine any environment, you will probably find a tardigrade there - they have an incredible resistance.

  'They've been tested in space, under liquid nitrogen, put under pressure and had chemicals thrown over them but they're fine after being washed in water.

  'Researchers even breed from the ones that were sent into space on European and American Agency missions.'

   Researchers led by Dr Roberto Guidetti from the University of Modena and Reggio Emilia in Italy found the new creature while on a trip to Victoria Land.

   Their examination under an electron microscope revealed various unusual features - including its red-orange body colour and cushions behind its claws.

   There was also a distinctive pattern of hairs on its body - suggesting the scientists were dealing with a new species.


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