Deep Subsurface Biosphere

1
Deep Subsurface Biosphere

• By Sara Cox

2
Outline

• History
• Deep Subsurface Biosphere
• SLiMEs
• Microbial Organisms
• TEAPs
• Anaerobic Degradation of Benzoate
• Sample-taking and Contamination
• Future
• References

3
History

• 1960s and 1970s discovery of microbes in
  geysers at temperatures of 160F
• 1981 Dr Stetter discovers hyperthermophiles in
  Icelandic hot springs
• 1989 first routine use of the term deep
  subsurface biosphere

4
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 15C per km, and
  reaches 110C at about 7 km depth
• Continental crust heats at 25C per km and
  reaches 110 C at 4 km
• Deepest samples recovered at 75C from a depth of
  2.8 km

5
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

6
Microbial organisms

• Hyperthermophilic methanogens at temperatures up
  to 110C or 6 km deep
• Subsurface microbes may be able to withstand
  temperatures up to 230F and possibly briefly to
  700 F, result of pressure
• Most terrestrial microbes die at the boiling
  point of water

7

• 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

8
(No Transcript)
9
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

10
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

11
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

12

• 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

13
(No Transcript)
14

• 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

15
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

16

• Untapped pool of genetic diversity
• Medical investigation of microbes for
  anti-cancer and anti-AIDS drugs
• Bioaugmentation pollution-eating bacteria for
  ground water cleanup
• Mary deFlaun (Envirogen) non-adhesive bacteria
• Storage of nuclear waste underground

17
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.