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
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

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 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

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 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

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

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- + 7H CH3COO- + HCO3- + 3H+ + CH2
Not thermodynamically favorable unless linked with aceoclastic methanogenesis
4C6H5COO+ + 18H 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

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 The Deep Hot Biosphere. Copernicus. New York.
Jones, R, Beeman, R. & Suflita, J Anaerobic Metabolic Processes in the Deep Terrestrial Subsurface. Geomicrobiology Journal 7 pg
Fredrickson, J. & Onstott, TC Microbes Deep Inside the Earth. Scientific American Oct
Lovley, D. Chapelle, F Deep Subsurface Microbial Processes. Reviews of Geophysics, 33,3.
Reysenbach, A. & Staley, J. ed 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