Endolith

The lifestyle of organisms as endolithisch inside of rocks called (old Greek ἔνδον endo "inside", " inside " and an ancient Greek λίθος lithos "stone" ). The endolithic life is only found in microorganisms, ie bacteria, archaea and some lichens, the latter represent a symbiosis between fungi and algae.

Endoliths usually live lithotroph, that is, they gain their necessary for life-energy from the conversion of inorganic compounds of the populated Gesteines, such as sulfur, iron and manganese compounds, in individual cases, but also minerals of uranium, arsenic and others. In addition, there phototrophic, ie photosynthetic endoliths. This is not a contradiction, because sunlight can penetrate deeply into certain rocks up to several millimeters. Especially quartz crystals such as granite or sandstone allow photosynthesis inside of rocks. The most common phototrophic endoliths are some lichens, as well as cyanobacteria Chroococcidiopsis. Great importance have iron and sulfur-oxidizing bacteria, because iron and sulfur are common elements of the earth's crust. In addition, many minerals are present as sulfur compounds. Widespread iron-sulfur minerals are pyrite and marcasite example. Bacteria, such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans can oxidize iron and sulfur under aerobic conditions. The microorganisms always compete here with the spontaneously occurring chemical reaction. However, they have enzymes that greatly accelerate this reaction in the cell by lowering the activation energy. Endoliths are therefore responsible for faster weathering and corrosion.

The sum formula for the chemical oxidation of iron-sulfur minerals is

FeS2 6 Fe ( H2O) 63 3 H2O → Fe2 S2O32 6 Fe ( H2O) 62 6 H

This reaction is catalyzed by ferric iron. The thiosulfate formed is not stable in acidic solutions, but is hydrolyzed to sulphate and other sulfur compounds. Divalent iron and reduced sulfur compounds then form potential energy sources for chemolithotrophic microorganisms. These regenerate the oxidant Fe 3 and thus accelerate the reaction. Within a short time considerable amounts of pyrite can be oxidized by this process. The formed sulfur dioxide and sulfuric acid causes a lowering of the pH value and in turn triggers other minerals from the rock. Leachates from mining dumps or flooded opencast mines are for this reason often to 3 severely acidified with pH values ​​of 2 and loaded with dissolved heavy metals. This effect is used in the bioleaching, a special mining method for low value ores advantage. Endoliths here serve as biocatalysts.

It has been isolated from the deepest mines in the world novel bacteria and archaea. Today, it is assumed that the depth of the biosphere is a largely unexplored habitat on earth and contains a considerable proportion of the biomass of our planet in the form of micro-organisms. These microorganisms are likely but usually grow slowly, because the underlying redox processes provide little energy. The most unusual endolithischer at the lithotrophic living organisms is that they get the only organisms completely without solar energy. Many are to grow in the position autotrophic, ie to bind carbon dioxide from their environment and to build organic matter only with the aid of chemical energy from purely inorganic compounds. Theoretically, such organisms exist on other celestial bodies.

The transition from endolithisch living organisms to soil organisms is often blurred. The isolation and characterization of endoliths is often difficult because these only occur at low cell densities, grow slowly and very specific demands on their environment, have some respect to temperature, pH, mineral composition and oxygen concentration.