Extreme habitats are those in which physical or chemical
conditions are so far from "normal" that they restrict microbial
diversity
Variables in extreme habitats include:
low water availability (Candida,
Torulopsis)
high salinity (1.5-4 M) selects for halophiles
(Halobacterium, Halococcus)
high acidity (pH ~ 3) selects for acidophiles
(Thiobacillus, certain Bacillus species,
Sulfolobus, Thermoplasma, some species of
methanogens)
high alkalinity (pH 10 or above) selects for
alkalophiles (some species of Bacillus, Micrococcus,
Pseudomonas, and some cyanobacteria)
high temperature (above 65C) selects for thermophiles
(Thermoplasma)
low temperature (below 10C) selects for
psychrophiles
high pressure selects for barophilic or barotolerant
organisms
Yellowstone National Park
Yellowstone National Park is located in an ancient
caldera ... the collapsed remains of a very large volcano
(prehistoric, of course) ... and it is characterized by the
presence of numerous hot springs, geysers and mud pots
many of the first Archaea described were discovered in
these thermal areas
because of the high mineral content of these
super-heated waters, there are many unusual lithotrophs
living here, especially thermophilic ones
due to the high sulfur content of these waters, one can
"see" the sulfur cycle in action in and around the hot
springs and mud pots
Water deeper than 1000 meters (more than 75% of all ocean
water) is considered to be the deep-sea
The deep-sea floor (except for
hydrothermal vents) is a biological wasteland, due to its:
low temperature (2-3C) - only psychrophiles
present
low nutrient levels - only oligotrophs present
high pressure - increases at the rate of 1
atmosphere (15 psi) for every 10 meters in depth (increased
pressure leads to decreased enzyme-substrate binding)
barotolerant organisms live at 1000-4000 meters
barophilic organisms live at depths greater than 4000
meters (generally dependent upon high pressure for growth if
found in water deeper than 10,000 meters)
Hydrothermal
vents are associated with ocean floor spreading centers -
very high temperatures (up to 380C in the vents themselves), very
high pressure and very high inorganic nutrient levels provide
conditions for unusual growth of mutualistic lithotrophic bacteria
and invertebrates (tubeworms and clams)
lithotrophic bacteria resembling Thiovulum
are the primary producers in an interesting mutualistic
association with tubeworms
trophosome (spongy tissue of the modified
gastrointestinal tract of tube worms) cells contain these
bacteria
endosymbiosis features:
hemoglobin of tube worm picks up hydrogen sulfide
as well as oxygen
hydrogen sulfide is transported to trophosome,
where it is utilized as bacterial energy source
oxygen also transported to trophosome, where
it is used as the final electron acceptor to support
sulfide oxidation by the bacteria
carbon dioxide from sea water is carbon source
for the lithotrophs (Calvin cycle present)
these tubeworms are organotrophs which live on
organic compounds generated by the bacteria
