Anhydrobiosis: Life without water

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AnhydrobiosisLife without water
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Water

• Solvent for all Biochemical reactions in cells.
• Essential for the maintenance of lipid bilayers
  (cell and organelle membranes).

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Without water you die!
Maintaining water balance is essential for life
or is it?
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How much can you lose?
of Body Water lost before death.
Humans 14
(Some) Frogs 50
Alpine Cockroaches 57
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Antony van Leeuwenhoek (1632-1723)

• Dutch microscopist
• Put the microscope to good biological use,
  discovering several phyla, Bacteria, sperm cells

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• on the third of September, about seven in the
  morning. I took some of the dry sediment, which
  I had taken out of the leaden gutter and had
  stood almost two days in my study, and put a
  little of it into two separate glass tubes,
  wherein I poured some rain water which had been
  boiled and afterwards cooled..

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• As soon as I had poured on the water, I stirred
  the whole about and when it had settled to the
  bottom of the glass, I examined it, and perceived
  some of the Animalcules lying closely heaped
  together. In a short time afterwards they began
  to extend their bodies, and in half an hour at
  least a hundred of them were swimming about the
  glass

van Leeuwenhoek, 1702
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Anhydrobiosis

• Life Without Water
• The ability to dry out completely and rehydrate
  again.
• Employed by small aquatic animals
  (micrometazoa), protozoa, bacteria and plants

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Some Anhydrobiotes

• Tardigrades (water bears)
• Nematodes
• Rotifers
• Springtails
• Midge Larvae

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Anhydrobiotic animals

• Are all small
• Have little/no control over water loss out of
  their body
• Are generally aquatic inhabitants of ephemerally
  wet habitats.

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Tardigrades

• Water Bears or Moss animals, live on the thin
  film of water on hydrated mosses, in soil, and in
  temporary pools.
• Many species are cosmopolitan, found from
  Greenland to Antarctica and everywhere in between.

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Polypedilum vanderplankii

• Midge larva
• Ephemeral pools in W. Africa
• Largest known anhydrobiont

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Drying Out 1. Buying Time

• Anhydrobionts must slow down the rate of water
  loss to allow them to make the necessary
  preparations

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Reducing sav ratio
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Structural changes

• As the animal shrinks, membranes fold and cell
  organelles are packed tightly together.

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Drying Membranes and Proteins

• The structure of membranes is dependent on the
  presence of water.
• Proteins also denature when dried, as their
  structure is also dependent on interactions with
  water
• If membrane structure is lost, then the animal is
  as good as dead

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TrehaloseThe magic sugar?
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Drying begins, coiling/contraction/Tun to reduce
rate of water loss.
100
Production of Trehalose Packing of cellular
organelles
Permeability slump
Fully Hydrated
Water content of Animal
gt99 of water gone
Anhydrobiotic
0
Time
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Once Dry

• Without water there can be no biochemical
  reactions
• Metabolism declines beyond detectable levels
  (0.01 of normal)

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While dry,

• No water left to freeze or boil
• No active cell processes to be disrupted

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Dry Insults

• Polypedilum vanderplanki can survive liquid
  helium temperatures (-262 ºC), and 102 ºC.
• Tardigrades can survive vacuum, radiation,
  anoxia, high temperatures (140 ºC) and high
  pressure (6000 atmospheres).
• Utsugi Noda (1995) found that Tardigrades could
  survive preparation for SEM!
• Tardigrades can survive in space!

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Rumours of Immortality

• Most anhydrobionts belong to groups that normally
  live only a few days or weeks but
• Tardigrades have recovered from herbarium
  specimens over 100 years old
• Some dry soils in Antarctica have not been wet
  for millenia
• Closer examination indicates that recovery is
  not survival, and there are no confirmed records
  of Tardigrades surviving more than 7 years.

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Anhydrobiosis in the Real World

• Anhydrobiosis is a genuine strategy for surviving
  extreme environments
• allows animals to survive long periods without
  water
• in this state they have increased tolerance to
  environmental extremes
• possibly also useful as a dispersal strategy.

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Scottnema lindsayae

• Soil Nematode found in McMurdo Dry Valleys,
  Antarctica.
• Acute shortage of water (almost no precipitation
  and very dry air)
• Very low temperatures in winter (lt-50 ºC)

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Scottnema lindsayae

• 80 of Nematodes are Anhydrobiotic at any given
  time.
• When Anhydrobiotic
• Dont grow or reproduce
• Survive all possible environmental conditions.

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Scottnema lindsayae

• When Fully hydrated, takes 280 days to complete
  life cycle.
• Water is not available all year
• Nematodes use a waiting strategy and develop only
  during periods of favourable conditions.
• How long to complete life cycle in field??

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Artemia cysts

• Live in salty, ephemeral habitats
• Eggs are layed and develop to gastrula (4000
  cells), encyst and dehydrate when water body
  dries up.
• Cysts rehydrate develop when wet

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Artemia cysts

• Easily stored and posted (Sea Monkeys, fish
  food)
• Survival of high temperatures essential as cysts
  may be on surface of depressions in deserts (eg
  California and Middle East)

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Anhydrobiosis on other worlds

• ?