Exploration of deep intraterrestrial microbial life: current perspectives

Abstract

Intraterrestrial life has been found at depths of several thousand metres in deep sub-sea floor sediments and in the basement crust beneath the sediments. It has also been found at up to 2800-m depth in continental sedimentary rocks, 5300-m depth in igneous rock aquifers and in fluid inclusions in ancient salt deposits from salt mines. The biomass of these intraterrestrial organisms may be equal to the total weight of all marine and terrestrial plants. The intraterrestrial microbes generally seem to be active at very low but significant rates and several investigations indicate chemolithoautotrophs to form a chemosynthetic base. Hydrogen, methane and carbon dioxide gases are continuously generated in the interior of our planet and probably constitute sustainable sources of carbon and energy for deep intraterrestrial biosphere ecosystems. Several prospective research areas are foreseen to focus on the importance of microbial communities for metabolic processes such as anaerobic utilisation of hydrocarbons and anaerobic methane oxidation. ß

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere

“…A bacterial and archaeal subsurface biosphere now is believed to have a near-global extent, being found in marine sediments; in the fractures and vents near midoceanic spreading centers; within older, cooled basaltic crust beneath the oceans; in deep aquifers of basalts and granitic batholiths; and in deep oil reservoirs of continental settings (51)(52)(53). Our results provide molecular fossil evidence for the existence of archaea in Late Archean sedimentary environments and in subsurface hydrothermal settings.…”

Microvirga subterranea gen. nov., sp. nov., a moderate thermophile from a deep subsurface Australian thermal aquifer

“…There is a plethora of evidence that microbial communities exist in the deep biosphere such as the deep sea (Pedersen, 2000). A limited number of other studies have reported the presence of microbial communities in the deep-bore-well biosphere but, as water samples were collected with the assistance of pumps (Stevens & McKinley, 1995) and soil samples by coring (Phelps et al, 1989), extraneous contamination could not be ruled out.…”

CO2 uptake by a soil microcosm

“…These prokaryotes use inorganic substrates to derive energy for biosynthesis reactions via aerobic or anaerobic CO 2 assimilation (Alfreider et al, 2009). They are unique in their ability to derive energy from sources not related to solar activity and can be found in diverse locations both above and below the Earths crust (Waksman and Joffe, 1922;Starkey, 1935;Pedersen, 2000;Amend and Teske, 2005;Sorokin and Kuenen, 2005;Alfreider et al, 2009). Microbial uptake of atmospheric CO 2 via autotrophic processes is a well characterised biological phenomenon, but actual estimations of sequestration rates are rare in the literature .…”