Transcript Deep Subsurface Biosphere

Deep Subsurface Biosphere
By Sara Cox
Outline
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History
Deep Subsurface Biosphere
SLiMEs
Microbial Organisms
TEAPs
Anaerobic Degradation of Benzoate
Sample-taking and Contamination
Future
References
History
• 1960’s and 1970’s: discovery of microbes in
geysers at temperatures of 160°F
• 1981: Dr Stetter discovers
hyperthermophiles in Icelandic hot springs
• 1989: first routine use of the term deep
subsurface biosphere
Deep Subsurface Biosphere
• Usually considered to begin 50m below surface of
the Earth and extend to variable depth
• Depth determined by maximum temperature
• Oceanic crust heats at a rate of 15°C per km, and
reaches 110°C at about 7 km depth
• Continental crust heats at 25°C per km and
reaches 110 °C at 4 km
• Deepest samples recovered at 75°C from a depth
of 2.8 km
SLiMEs
• Subsurface lithoautotrophic microbial ecosystems
• fluid-filled pores, cracks and interstices of rock
and feed off heat and chemicals, main microbial
habitat is in hot aquifers under continents and
oceanic abyssesIf 1% of total pore space was
occupied, the mass of microbes would be 200
trillion tons, enough to coat land surfaces 5 feet
thick
Microbial organisms
• Hyperthermophilic methanogens at
temperatures up to 110°C or 6 km deep
• Subsurface microbes may be able to
withstand temperatures up to 230°F and
possibly briefly to 700 °F, result of pressure
• Most terrestrial microbes die at the boiling
point of water
• Bacteria, archaea and eukaryotic
microorganisms are all well distributed,
with the exceptions of algae and ciliates
• High clay layers have low microbial
numbers but sandy layers have elevated
numbers
TEAPs
• Terminal electron accepting processes
• The most common TEAPs are O2, nitrate,
Mn (IV), Fe (III), sulfate and CO2
• Distribution of TEAPs in deep aquifers
occur in this order: oxic, nitrate and Mn(IV)
reducing, Fe(III) reducing, sulfate reducing
and finally methanogenic
Anaerobic degradation of
benzoate
• C6H5COO- + 7H20 3CH3COO- + HCO3- +
3H+ + CH2
• Not thermodynamically favorable unless
linked with aceoclastic methanogenesis
• 4C6H5COO+ + 18H20 15 CH4 +13CO2
• Anaerobic degradation of phenol is also
linked with acetoclastic methanogenesis
Sample-taking and
Contanimation
• Debate: are subsurface microbes actually
indigenous or are they merely surface
contaminants?
• Lack of photosynthetic organisms in
samples
• Specialized drilling and sample-collecting
to try to prevent contamination
• Nitrogen or argon gases used in in drilling
rather than fluids
• Sterilized drilling fluid or tracers
• Sterile and non-oxidizing containment of
samples
• Argon-filled bags enclose all tools and
samples kept in boxes of argon or nitrogen
• If non-oxidizing gases are not used in
drilling, drilling fluids are often marked
with tracers (fluorescent or organically
labeled)
• When samples are taken either completely
untagged samples are used or the
contaminated layers are removed and the
“clean” areas are inspected
Future
• Possible life on other planets? T. Gold
predicts at least 10 possible deep biospheres
in our solar system
• Drilling not feasible, collection of samples
from deep layers that are now exposed, ex.
Valley Marinara on Mars, once several km
deep
• Untapped pool of genetic diversity
• Medical: investigation of microbes for anticancer and anti-AIDS drugs
• Bioaugmentation: pollution-eating bacteria
for ground water cleanup
• Mary deFlaun (Envirogen) non-adhesive
bacteria
• Storage of nuclear waste underground
References
Gold, Thomas. 1999. The Deep Hot Biosphere. Copernicus. New York.
Jones, R, Beeman, R. & Suflita, J. 1989. Anaerobic Metabolic Processes
in the Deep Terrestrial Subsurface. Geomicrobiology Journal 7 pg.
117-130.
Fredrickson, J. & Onstott, TC. 1996. Microbes Deep Inside the Earth.
Scientific American Oct. 1996.
Lovley, D. Chapelle, F. 1995. Deep Subsurface Microbial Processes.
Reviews of Geophysics, 33,3.
Reysenbach, A. & Staley, J. ed. 2002. Biodiversity of Microbial Life.
Wiley-Liss, Inc. New York.
Sinclair, J. & Ghiorse, W. Distribution of Aerobic Bacteria, Protozoa,
Algae, and Fungi in Deep Subsurface Sediments. Geomicrobiology
Journal 7. Pg. 15-31.