BACK TO 1i: PRESENTING THE FINDINGS
bacteriologist Thomas Brock started probing the hot springs in Yellowstone
National Park in the 1960's, he wasn't looking to overthrow a ground
rule of biology but
to study bacteria in a simplified, real-world environment. As the
University of Wisconsin-Madison professor sampled his way up a hot
stream, he approached the hot spring supplying it and the water got
warmer and warmer. At the time, biologists thought life would not
tolerate temperatures anywhere near 80 degrees Celsius, but Brock
kept finding bacteria, so he kept on looking. Eventually, he found
organisms that could live and reproduce near the temperature of boiling
water (100 degrees C).
ERIC: The prize
of his collection was an organism he named Thermus aquaticus and was
deposited in a public repository for study
by other scientists. Over the years, Thermus aquaticus proved to be
very interesting. It was one of at least 50 species of thermophilic
bacteria which could tolerate or require temperatures near water's
boiling point. It was also the first of the Archaea, ancient microorganisms
that some scientists now regard as a separate kingdom of life.
include inhabitants of some of the most extreme environments on the
planet. Some live near rift vents in the deep sea temperatures well
over 100 degrees Celsius. Others live in hot springs, in extremely
alkaline or acidic waters, or in extremely saline water. Archaeans
may be the only organisms that can live in extreme habitats such as
thermal vents or hypersaline water. They may be extremely abundant
in environments that are hostile to all other life forms. However,
archaeans are not restricted to extreme environments. New research
shows that archaeans are also quite abundant in the plankton of the
ERIC: There are
3 main types of Archaeans: Methanogens, Halophiles, and Thermoacidophiles.
Methanogens are found in anaerobic environments such as the muck of
swamps and marshes, the rumen of cattle, sewage sludge, and the gut
of termites. They are autotrophic and use hydrogen as a source of
electrons for reducing carbon dioxide to food and give off methane
as a byproduct. Halophiles are found in extremely saline environments
such as the Great Salt Lake and the Dead Sea. They maintain osmotic
balance with their surroundings by building up the solute concentration
within their cells. Thermoacidophiles are found in such places as
acidic sulfur springs and undersea vents and like hot temperatures
and acidic surroundings.
�pH' is used to denote the relative acidity or alkalinity of water.
Water which is exactly neutral has a pH of 7; waters which are acid
have a pH of less than 7, and waters which are alkaline have a pH
greater than 7. Most acid springs in Yellowstone have a pH between
2 and 4. The neutral-alkaline springs have a value from 7 to 9. The
ranges for particular pools in Yellowstone is shown on this chart.
In several of
the acidic hotsprings in Yellowstone, thermoacidophilic prokaryotes
in the domain Archaea are the only known inhabitants. The prokaryotes
are the genera Sulfolobus or Acidianus. Both these genera contain
organisms which oxidize elemental sulfur to sulfuric acid and use
this energy to grow autotrophically, using carbon dioxide as their
carbon source. This chart shows the various pH limits for organisms
- the lowest they are known to be able to live in.
I'm going to try to answer the question: how hot can the surroundings
be for living organisms?
In general, plants
can grow at temperatures no higher than 50 degrees Celsius (122 F).
Plants can survive higher temperatures, but they will not be able
to grow or reproduce, only survive. Animals - that is, multicellular
organisms - are similar. Their limit is around 50 degrees Celsius
- they can survive higher, but not live or grow in environments that
are constantly that high.
are different - they can grow in temperatures much higher than that.
Many microorganisms can live in temperatures well above 50 Celsius,
in fact up to 115 Celsius, which is past the boiling point of water
at sea level. Only the organisms in the domain Archaea are able to
Here is a graph
showing maximum temperature ranges. You can see plants and animals
live in temperatures up to 122 F. But one of the organisms that lives
in the Yellowstone hot pots, Sulfolobus acidocaldarius, lives in temperatures
up to 194 F, and doesn't live in temperatures below 158 F. And another
organism in the hot pots, Pyrobacterium brockii, lives in temperatures
up to 239 F, and doesn't live in temperatures below 176 F.
we took a trip to Yellowstone, to observe some biologists and a geologist
as they took samples of the microorganism Sulfolobus acidocaldarius
to take back to the lab. Here are pictures of the biologists measuring
the temperature and pH of the hot pots... scooping up samples of the
water in the hot pots... and labeling their samples, and treating
them so the microorganisms will survive the journey back to the lab.