Deep Subsurface Biosphere By Sara Cox

Outline 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 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

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.