T
ardigrades (also known as water bears or moss piglets)
are water-dwelling, eight-legged, segmented microscopic
(body size from 0.05 to 1.2mm) invertebrates. They were first
discovered by the German pastor Johann August Ephraim Goeze in
- Italian biologist Lazzaro Spallanzani named them Tardigrada
meaning slow stepper. They can be found throughout the world,
from the Himalayas above 6,000 m (20,000 ft), to deep sea (below
4,000 m (13,000 ft)) and from the polar regions to the equator.
Tardigrades are notable for being perhaps the most durable
of known organisms. They are able to survive extreme
temperature ranges from 1K (–458°F; –272°C) to about
420K (269°F; 147°C), pressures about six times greater
than those found in the deepest ocean trenches, ionising
radiations at doses hundreds of times higher than the
lethal dose for a human, and the vacuum of outer space.
They can go without food or water for more than 30 years,
drying out to the point where they are 3% or less water.
They are not considered as true extremophiles because they
are not adapted to exploit these conditions. This means that
their chances of dying increase, the longer they are exposed to the
extreme environments.
During desiccation, tardigrades can dry out completely, replacing
almost all the water in their bodies with a sugar called trehalose. As
a result, they’re able to survive environments that would otherwise
kill them. Scientists have discovered that to survive extreme
desiccation, tardigrades produce a special type of ‘bioglass’ to hold
essential proteins and molecules together until they’re rehydrated
back to life.
Researchers from the University of Chicago discovered a new type
of glass produced internally by the tardigrades during desiccation.
They concluded that the glass is produced as a protective
mechanism to ensure that tardigrades can survive losing pretty
much of all the water in their cells.
During desiccation, they very quickly coat themselves in large
amounts of glassy molecules.
According to another group of researchers, Boothby and his
colleagues, tardigrade—specific genes code for specialised
proteins called intrinsically disordered proteins (IDPs), which are
responsible for the production of tardigrade glass. Intrinsically
disordered proteins are shapeless and highly flexible under normal
conditions, but when extreme drying occurs, the production of
these proteins is kicked up, and they rearrange themselves into solid
biological glasses. These newly formed IDP glass structures target
specific proteins, molecules and other essential cell parts when the
tardigrades start losing water, and enclose them in stiff, protective
envelopes so they don’t fall apart during the desiccation process.
When the tardigrade is exposed to water once more, the glass melts
and the IDPs return to their floppy, random state.
TARDIGRADES - THE MOSTDURABLE ORGANISMS
meaning slow stepper. They can be found throughout the world,
from the Himalayas above 6,000 m (20,000 ft), to deep sea (below
4,000 m (13,000 ft)) and from the polar regions to the equator.
Tardigrades are notable for being perhaps the most durable
of known organisms. They are able to survive extreme
They are not considered as true extremophiles because they
are not adapted to exploit these conditions. This means that
their chances of dying increase, the longer they are exposed to the
Boothby and his colleagues also found that at lower levels of
IDPs these tardigrades were less able to withstand desiccation
but remained unaffected by other stresses such as extreme cold.
So, they suggest that the creatures have different mechanisms to
survive different types of extreme stresses.
According to researchers, foreign DNA has allowed the water bear
to survive in such extreme conditions. Scientists on sequencing the
whole genome of the tardigrades, suggest that tardigrades have
most foreign genes of any animal studied so far.
Foreign DNA have presumably come from another organism via
a process known as horizontal gene transfer, as opposed to being
passed down through traditional reproduction. The foreign DNA
comes primarily from bacteria, but also from plants, fungi and
Archaea. During desiccation tardigrades’ DNA breaks down into
tiny pieces. When their cells rehydrate, there is a point in time when
the cell nucleus is leaky, allowing DNA and other molecules to pass
through. That means that while the tardigrade is quickly patching
up its own genome, it may accidentally be stitching in another
organism’s genes.
This drying or freezing out of water bears during extreme conditions
is a peculiar form of existence known as cryptobiosis or anabiosis.
Their cryptobiotic properties helped scientists to develop so called
‘dry vaccines’. In such vaccines water is replaced with trehalose.
Dry vaccines don’t require refrigeration and thus can be delivered
and stored at room temperature in the most remote developing
countries in the world.