VIII. Temperature Extremes
How hot do Pompeii worms get? There was a paper in Nature that came
from some work by Jim Childress and two French colleagues who found a Pompeii
worm sitting in water which they measured at 105 degrees. That certainly
is hotter than any animal is known to tolerate. The worm eventually got
up and swam away so they weren't looking at a worm that was being barbecued.
They were looking at a worm that was actually able to survive at least a
short term exposure to these high temperatures.
In
this week's Nature, there is a paper from Craig Carey and colleagues
on temperatures inside a Pompeii worm's tube. What they did was to insert
into Pompeii worm tubes, a thermistor that allowed them to make a transect
along the whole length of the worm's home. They found that they could insert
this probe into a tube without scaring the worm out.
What they found was that at the far ends of the tubes, in other words the part
of the Pompeii worms' tube that was deepest in a black smoker chimney nearest
the spire of hot vent water, temperatures ran around 81 degrees Celsius.
At the other end of the tube where the worm's head and gills would be, the
temperatures averaged around 22 degrees. Here is an animal that has roughly
a 60 degree temperature gradient along it's body surface. Now, that's not
to say that the worm's tail is at 81 degrees Celsius and it's schnozzola
is at 22 degrees Celsius. The worm has a very good circulatory system. Thus,
there is probably going to be a very large distribution of heat throughout
the worm. The worm loses heat in its gills, which are exposed to 22 degree
water, and sends cool blood back into the body of the animal. None-the-less,
this is an animal that's seeing an enormously large temperature gradient
outside its body surface. Our guess is that the worm is probably seeing
an average internal temperature in the range of 40-50 degrees. That's about
as hot as any animal has ever been found to be.
Looking
at the black smoker chimneys again, these are the chimney walls in which
the Pompeii worms are found. People have tried to see what the upper temperature
limits of life are. There are workers in Germany, Karl Stetter is one of
the leaders in this field, who have taken water samples from the black smoker
chimneys and other sites where temperatures are unusually high. They've
tried to culture bacteria from these different water samples. What they
found is very interesting. It looks as if temperatures between 110 degrees
Celsius and 115 degrees Celsius are the upper temperature limits for life.
The organisms that have been cultured at high temperatures, "extremeophiles"
as they're called, seem to be able to tolerate temperatures up to about
113 degrees Celsius, but no higher. Obviously, these cells have to be grown
under high pressure in order to keep the culture medium liquid.
|
|
|
Narrative Index
BioForum Index
