The document discusses hot springs and the organisms that can live in extremely hot conditions. It explains that hot spring water is heated either by geothermal heat from within the Earth or, in volcanic areas, by contact with magma. It also describes some of the microbes that have been found living in hot springs, including various archaea, bacteria, and viruses that are able to thrive at temperatures over 100°F. The discovery of these thermophilic organisms expanded the understanding of what was believed to be the maximum temperature limit for life.

4. •The water issuing from a hot spring is heated by geothermal heat, essentially heat from
the Earth's interior. In general, the temperature of rocks within the Earth increases with
depth. The rate of temperature increase with depth is known as the “geothermal
gradient”. If water percolates deeply enough into the crust, it will be heated as it comes
into contact with hot rocks. The water from hot springs in non-volcanic areas is heated in
this manner.
•In volcanic zones, such as Yellowstone National Park, water may be heated by coming
into contact with magma (molten rock). The high temperature gradient near magma
may cause water to be heated enough that it boils or becomes superheated. If the water
becomes so hot that it builds steam pressure and erupts in a jet above the surface of the
earth, it is called a geyser; if the water only reaches the surface in the form of steam, it is
called a fumarole; and if the water is mixed with mud and clay, it is called a mud pot.
There are no geysers, fumaroles, or mud pots at Hot Springs National Park.
One thermophile, Pyrolobus fumarii, has been
found at temperatures of
113° C /235° F

6. Vocabulary words
aquifer - a water-bearing stratum of permeable rock, sand, or gravel
calcareous - resembling calcite or calcium carbonate especially in hardness; consisting of
or containing calcium
chert - rock resembling flint and consisting of quartz and amorphous silica
fault - a fracture in the crust of the Earth accompanied by a displacement of one side of
the fracture with respect to the other, usually in a direction parallel to the fracture
fissure - a narrow opening or crack of considerable length and depth usually occurring
from some breaking or parting
gradient - change in the value of a quantity (as temperature, pressure, or concentration)
with change in a given variable and especially per unit distance in a specified direction
hybrid - an offspring of two animals or plants of different
races, breeds, varieties,species, or genera
hydrothermal - of or relating to hot water
isotope - any of two or more atoms of a chemical element with the same atomic number
and nearly identical chemical behavior but with differing atomic mass or mass numberand
different physical properties

7. magma - molten rock material within the Earth from which igneous rock results by
cooling
meteorite - any of the small particles of matter in the solar system that are directly
observable only by their incandescence from frictional heating on entry into the
atmosphere
novaculite - a very hard fine-grained siliceous chert used for whetstones
percolate - to ooze or trickle through a permeable substance
protozoa - any of a phylum or subkingdom (Protozoa) of chiefly motile and
heterotrophic unicellular protists (as amoebas, trypanosomes, sporozoans, and
paramecia) that are represented in almost every kind of habitat
pseudopod - temporary protrusion or retractile process of the cytoplasm of a cell that
functions (as in an amoeba) especially in a locomotor or food gathering capacity
seismic - of, subject to, or caused by an earthquake; or relating to an earth vibration
siliceous - of, relating to, or containing silica
suspension - the state of a substance when its particles are mixed with but undissolved
in a fluid or solid
tufa - a porous rock formed as a deposit from springs or streams

10. History: Pre 19th Century
• Believed aquatic plants and
animals cannot live at
temperatures above 37˚C
• 1862 – Ferdinand Cohn first
observed organisms living in
hot springs in Sicily, Italy
• 1875 – Felix Hoppe-Seyler
recorded algae in hot springs
in Naples, Italy at
temperatures above 60˚C

11. History 1900 to Present
• 1903 – William Setchell observed
algae in hot springs at ~ 75˚C and
89˚C in Yellowstone National Park
• 1978 – Thomas Brock found
cyanobacteria in hot springs at 75-
77˚C, and observed growth at
temperatures up to 95.5˚C
• Early 1990s –Thermus aquaticus
discovered, utilized this
organism’s thermotolerant
polymerase (“Taq”) in PCR
reactions
• Recently – discovery of
archaea, bacteria and viruses in
hot springs continue

12. General Hot Springs Ecology
• Photosynthetic
microorganisms dominate,
ranging from 102 to 108/ml,
found mostly in euphotic
surface layers or on rock
surfaces
• Heterotrophic
microorganisms are also
found, but in lower
concentrations (101 to
106/ml), and consume DOM
from terrestrial and
biological sources (dead
photosynthetic organisms)

13. Archaea
Most archaea grow at temperatures of 80-85ºC
• Methanogens (Methanobacterium thermophilicum)
• 2 distinct lineges present? in Yellowstone hot springs
(small-subunit rRNA analysis)
• A little is known; research continues.
A microbiologist collecting
water sample at Yellowstone
hot spring.

14. Bacteria I
• Cyanobacteria (Synechococcus)
– Thermophile photoynthetic
autotrophs
– Grow up to 74ºC.
– “Algal mat” (Yellowstone)
• Many distinct species living in
vertically stratified mats based
on 16S rRNA phylogenetic
studies
Algal mat in Yellowstone

15. Bacteria II
• Heterotrophic bacteria (thermophiles)
• Chemolithotrophs
– H2S & sulfur oxidizers (e.g. Thiobacilus
thiooxidans, Sulfolobus acidocaldarius: found in
highly acidic hot springs)
– Sulfate reducers (e.g. Desulfovibrio thermophilus)
– Methane oxidizers (e.g. Methylococcus capsulatus)

16. Viruses
Electron micrographs of
viruses found in Little
Hot Creek, OR (Breibar
et al. 2004)
• Absence of eukaryotes… but viruses are there
• Thermophilic bacteriophages observed living at up to
92ºC: extreme thermophiles
• Predators of bacteria
• “Microbial loop” in hot springs

17. ml TT media (ATCC medium 697