page_title: Deep biosphere
section_title: Ecology
hierarchical_section_title: Deep biosphere / Ecology
caption_attribution_description: English: Electron micrograph with cells identified as "Candidatus Desulforudis audaxviator"
context_page_description: The deep biosphere is the part of the biosphere that resides below the first few meters of the surface. It extends down at least 5 kilometers below the continental surface and 10.5 kilometers below the sea surface, at temperatures that may reach beyond 100°C. It includes all three domains of life and the genetic diversity rivals that on the surface.
  The first indications of deep life came from studies of oil fields in the 1920s, but it was not certain that the organisms were indigenous until methods were developed in the 1980s to prevent contamination from the surface. Samples are now collected in deep mines and scientific drilling programs in the ocean and on land. Deep observatories have been established for more extended studies.
  Near the surface, living organisms consume organic matter and breathe oxygen. Lower down, these are not available, so they make use of "edibles" such as hydrogen, methane, reduced sulfur compounds and ammonium. They "breathe" electron acceptors such as nitrates and nitrites, manganese and iron oxides, oxidized sulfur compounds and carbon dioxide.
context_section_description: One species of Bacteria, "Candidatus Desulforudis audaxviator", is the first known to comprise a complete ecosystem by itself. It was found 2.8 kilometers below the surface in a gold mine near Johannesburg, South Africa. In alkaline water at a temperature of about 60°C, with no access to oxygen, it gets energy by reducing sulfate, its nitrogen from ammonia molecules and ammonium ions, and its carbon from carbon dioxide or formate.
  Other ecosystems have multiple interdependent species. They can be divided into autotrophs, which derive energy from non-living sources, and heterotrophs, which feed on autotrophs or their remains. Some organisms engage in syntrophy, where one organism lives off the byproducts of another's metabolic activity. At the surface, most autotrophs use photosynthesis, but where there is no light, chemoautotrophs make use of chemical energy.
  In marine sediments where oxygen is available, a major group of chemoautotrophs is ammonia-oxidizing Thaumarchaeota. It supports 19% of the heterotrophic production. In some environments such as abyssal Pacific Ocean sediments, the supply of ammonia dwindles with depth; but in other environments ammonia actually increases because heterotrophic bacteria, living on organic material, remineralize the ammonia. This interdependence of the heterotrophic bacteria and Thaumarchaeota is an example of syntrophy. However, some Thaumarchaeota are mixotrophic, able to use both organic matter and carbon dioxide for carbon.
  In anoxic sediments, hydrogen is an important "edible". Members of the Chloroflexi draw energy from it to produce acetate by reducing carbon dioxide or organic matter (a process known as acetogenesis). Metal-reducing and sugar-fermenting Bacteroidetes produce propionate, among other compounds, and this is fermented by "Ca. Atribacteria" to produce hydrogen. In upper sediments, sulfate-reducing bacteria take up most of the hydrogen, while in lower sediments the sulfate is depleted and methanogens dominate. In the sulfate-methane transition zone (SMTZ), anaerobic methanotrophic (ANME) archaea form consortia with sulfate-reducing bacteria.
caption: The purplish rod-shaped cells, a few microns long, are "Candidatus Desulforudis audaxviator".[15]
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