Geomicrobiology

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The geomicrobiology ( ancient Greek γῆ , ge "earth", μικρός , mikros "small", βίος , bios "life" and λόγος , logos , "word") is a branch of microbiology . It mainly deals with the influences of microbial metabolic processes on the nature of the surface layers of the earth ( earth's crust with lithosphere and hydrosphere as well as atmosphere ) and with the properties of the microorganisms concerned . Both the current influences and those of the earth's history are dealt with.

Geological stratification of the earth's crust

Particular importance of microorganisms for geochemistry

The influences of microorganisms on the condition of the earth's surface are of particular importance in both quantitative and qualitative terms. This is due to the following peculiarities of microorganisms compared to larger living beings :

  • According to estimates, the mass of the microorganisms is about as large or even greater than that of all other living things .
  • Since microorganisms have a large specific surface (based on their mass, surface-volume ratio ) due to their small size and the greater their specific surface, the greater the metabolic speed of living beings, microorganisms are characterized by a specific, mass-related Metabolic rate, which is orders of magnitude higher than that of larger living things. The large biomass of microorganisms on earth and the high specific metabolic rate are the reasons why the metabolic processes of microorganisms are quantitatively of particular importance for the geochemical nature of the earth's surface.
  • Microorganisms are characterized by a greater qualitative diversity of metabolism than larger living beings: They cause many chemical conversions that other living beings are not capable of, for example formation of methane and hydrogen sulfide , oxidation of ammonia and hydrogen sulfide.
  • Some microorganisms, especially bacteria, are adapted to extreme environmental conditions (so-called " extremophiles "). For example, they can grow in a strongly acidic or alkaline environment (pH 1 or 11) or at temperatures of up to 120 ° C or 4 ° C or at pressures above 1000 bar (above 100 MPa).

Geochemically significant microbial metabolism

Below are some examples of microbial metabolism that are of particular importance for the geochemical nature of the near-surface layers of the earth:

  • Consumption of carbon dioxide (CO 2 ) to the formation of biomass (CO 2 - Assimilation ). In addition to lowering the CO 2 concentration in water bodies and in the atmosphere, the result is an alkalization (increase in pH value ) of water bodies and thus a precipitation of calcium carbonate (CaCO 3 ) and the formation of limestone .
  • Incorporation of calcium carbonate (CaCO 3 ) in skeletons (especially in coccolithophores and foraminifera ) and thus formation of limestone.
  • Incorporation of silicon dioxide (SiO 2 ) in skeletons (especially in diatoms and radiolarians ) and thus formation of SiO 2 rocks, for example silica slate after diagenesis .
  • Formation of methane (CH 4 ) (by methanogenic archaea ), which acts as a “ greenhouse gas ”.
  • Oxidation of bivalent iron (Fe 2+ ) and thus immobilization of iron in the form of compounds of trivalent iron.
  • Reduction of trivalent iron and mobilization of iron from substantially water-insoluble compounds in the form of Fe 2+ - ion .
  • Oxidation of hydrogen sulfide (H 2 S) and elemental sulfur to sulfuric acid and thus acidification of the environment
  • Dissolution of heavy metal sulfides ( e.g. pyrite and marcasite , both FeS 2 ) by abiotic oxidation of the sulfide by ions of trivalent iron and biotic oxidation of the elemental sulfur and the sulfur compounds formed as well as biotic reoxidation of the divalent iron ions to trivalent ones; The consequence of the processes is the dissolution of the sulphide minerals and the mobilization of the heavy metals.
  • Reduction of sulphates to hydrogen sulphide (H 2 S) by sulphate-reducing bacteria with the result that heavy metals are precipitated as practically water-insoluble sulphides and are thus immobilized.

Microorganisms and geochemical earth evolution

Microorganisms have been colonizing the earth for at least 3.8 billion years , while larger, multicellular living things have only been around 0.7 billion years . Due to their metabolism, microorganisms had a significant influence on the geochemical development of the near-surface layers of the earth (earth's crust with hydrosphere and lithosphere as well as atmosphere) very early on:

  • Drastic reduction in the content of carbon dioxide (CO 2 ), which was the main component of the atmosphere at the beginning and was therefore also contained in high concentrations in the hydrosphere, through CO 2 assimilation (binding of carbon in biomass). This alkalization of the seas, precipitation of carbonates and the formation of limestone.
  • Formation of elemental oxygen (O 2 , dioxygen), which is initially only present in very low concentrations , through oxygenic photosynthesis . This resulted in drastic changes in the hydro- and lithosphere as well as consequences for the evolution of living things.
  • Immobilization of divalent iron, which was initially dissolved in the oceans as Fe 2+ ions, by oxidation to trivalent iron, which was precipitated in the form of Fe (III) compounds and ultimately converted into hematite (Fe 2 O 3 ) (formation of "Banded iron stones", " Bändererz " English "Banded Iron Formations" = "BIF" and of red sandstones , "Red Bed").
  • Formation of water sparingly soluble sulfates such as calcium sulfate ( gypsum , anhydrite ) and barium sulfate ( barite ).

See also : endoliths , microbiology

literature

  • Manfred Köhler, Fernando Völsgen: Geomicrobiology - Basics and Applications . Wiley-VCH, Weinheim et al. O. 1998, ISBN 3-527-30083-X
  • Henry Lutz Ehrlich, Dianne K. Newman: Geomicrobiology . 5th edition. CRC Press, Boca Taton 2009, ISBN 978-0-8493-7906-2
  • Tom Fennel, Gary M. King, Thomas Henry Blackburn: Bacterial biogeochemistry: The ecophysiology of mineral cycling . 2nd Edition. Academic Press, London et al. O. 1998, ISBN 0-12-103455-0

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