Brine shrimps have the ability to revive after years without oxygen
under unfavourable - oxygen-deprived - conditions, brine shrimps shut down their energy processes and enter a death-like state; but when favourable conditions are restored, perhaps years later, these animals rise up, hatch and swim away, says James Clegg, a biochemist at the University of California's Bodega Marine Laboratory in Bodega Bay, us. This remarkable activity challenges one of biology's fundamental assumptions - that energy processing is an essential feature of life (New Scientist, Vol 153, No 2068).
In harsh conditions, brine shrimps form a resistant cyst that helps them overcome the tough surroundings. This might happen, for example, when a pond dries up in summer or becomes deficient of oxygen due to the presence of certain bacteria. Clegg carried out experiments on this by keeping a few cysts in oxygen-free vials of water for four years. He observed that more than 60 per cent of the shrimps hatched once the oxygen was restored. However, hatching took much longer - a week or more - as compared to a day or two for cysts that never experienced anaerobic (oxygen-deprived) conditions.
But surprisingly, the shrimps did not utilise any energy during the period of their 'suspended animation'. Their carbohydrate stores, which are their only source of metabolic energy, showed no detectable change during this period. "Cells do need to process energy to make proteins and repair damage," says Clegg. Yet his experiments showed that this need not always be the case. This deprivation did not even harm the hatchlings. After the revival of oxygen, they survived as long as those that were never deprived of oxygen. "If you cannot measure the metabolic activity you associate with life, it makes one start thinking about how to define life and death," says Steven Hand, a biochemist at the University of Colorado in Boulder, us.
A few other animals have been known to survive for hundreds of years under dried or frozen conditions. But under such a situation, one would expect their proteins to gradually dete-riorate unless the organism expended energy to repair them. Even by using radioactive labeled proteins, Clegg found no evidence of protein breakdown for over a year in encysted shrimps. "They have found a way to escape this, and I would like to know what that is," says Clegg. The answer may involve proteins called 'chaperones', which can bind to other proteins and protect them from damage, though Clegg has yet to prove that it plays a similar role in living brine shrimps.
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