It is known that Antarctica is one of earth’s harshest environments, challenging its inhabitants with extreme cold and drought, requiring extreme adaptation mechanisms. However, a lot of organism have adapted to live in freezing conditions, but not many are able to survive intracellular ice formation . An example of this is Panagrolaimus davidi, a bacterial feeding anhydrobiotic nematode.

Panagrolaimus sp. lives associated with moss and algae in on the Victoria Land coast, that are free of snow and ice for part of the year. It has to survive very variable thermal and hydric conditions, where water and temperatures suitable for growth are only periodically available. Panagrolaimus sp.  can survive complete water loss  and is the only organism that has been shown to survive intracellular ice formation throughout its tissues. Usually  intracellular ice formation is fatal due to the danger of puncturing membranes by ice crystals and the of ice crystals after freezing and during defrosting.

Panagrolaimus sp. specimens. Picture by David Wharton

Recent study in the Antarctic shows the capacity of Panagrolaimus sp.  to not only withstand ice formation intracellularly and survive, but also been able to produce progeny once defrosted.

Unlike other organisms that can live in low temperatures, there is no evidence to show that Panagrolaimus sp. possesses ice-active proteins. Therefore how this animal can survive intracellular freezing still a mystery. Researches has been working in this topic for plenty of time and they realize that, by exploring patterns of gene expression, This nematodes are molecularly active in the frozen state, highlighting certain key genes that allow them to withstand such extreme physical state.

So, how is it possible that this nematode survives to intracellular freezing? Well this still a not fully understood. For now it is known that Panagrolaimus sp. uses a cryoprotective dehydration technique, which means that if freezing of the nematode’s surroundings occurs at a high sub-zero temperature, the inside of the organism stays unfrozen. Then water is lost to the surrounding ice, leaving the organism with no water to be froze. However, even if Panagrolaimus sp. is cooled faster, it is frozen while hydrated can experience intracellular ice formation and survive. So this nematode has more than the usual techniques to maintain life while intracellularly frozen, which now still unknown.

Freezing in P. davidi (from Wharton and Ferns, 1995 )

The most accepted answer, conclude by Wharton (2003) is that  the extreme cold tolerance of  Panagrolaimus sp. compared to other nematodes may be a combination of rapid freezing, trehalose production and a recrystallization inhibiting ice-active protein. However, this protein has not been synthesize in lab studies yet.

Panagrolaimus sp. is the most studied nematode that can survive freezing, but nobody has proved the technique that this worm uses to survive to intracellular freezing.

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