Endolites

from Wikipedia, the free encyclopedia
Endolithic lichen of the genus Verrucaria

The way of life of organisms inside rocks is called endolithic (from ancient Greek ἔνδον endon , German 'inside' and λίθος lithos , German 'stone' ). The endolithic way of life is only found in microorganisms , i.e. bacteria , archaea and some lichens , the latter representing a symbiosis between fungi and algae .

Endoliths are mostly lithotrophic , which means that they gain the energy they need for life from the conversion of inorganic compounds in the populated rock, such as sulfur , iron and manganese compounds , but in some cases also minerals of uranium , arsenic and others.
In addition, there are phototrophic , i.e. photosynthesizing , endoliths. This is not a contradiction in terms, as sunlight can penetrate certain rocks up to several millimeters deep. Quartz crystals in particular, such as those found in granite or sandstone, enable photosynthesis inside rocks. The most common phototrophic endoliths are some lichens, but also cyanobacteria such as Chroococcidiopsis .
Iron and sulfur oxidizing bacteria are of great importance because iron and sulfur are common elements in the earth's crust. In addition, many minerals are present as sulfur compounds. Common iron-sulfur minerals include pyrite and marcasite . Bacteria such as Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans to iron and sulfur under aerobic conditions oxidize . The microorganisms always compete with the spontaneous chemical reaction . However, they have enzymes that considerably accelerate this reaction in the cell by reducing the activation energy . Endoliths are therefore responsible for faster weathering and corrosion .

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

FeS 2 + 6 Fe (H 2 O) 6 3+ + 3 H 2 O → Fe 2+ + S 2 O 3 2− + 6 Fe (H 2 O) 6 2+ + 6 H +

This reaction is catalyzed by trivalent iron. The thiosulfate formed is not stable in acidic solutions, but hydrolyzes to sulfate and other sulfur compounds. Bivalent iron and reduced sulfur compounds then form potential energy sources for chemolithotrophic microorganisms. These regenerate the oxidizing agent Fe 3+ and thus accelerate the reaction. This process can oxidize considerable amounts of pyrite within a short time. The sulfuric acid and sulfuric acid formed cause the pH value to drop and, in turn, dissolve other minerals from the rock. For this reason, seepage water from mining dumps or flooded open-cast mines is often strongly acidic with pH values ​​of 2 to 3 and contaminated with dissolved heavy metals . This effect is used in bioleaching , a special mining process for low-value ores . Endoliths serve as biocatalysts .

Novel bacteria and archaea have been isolated from the deepest mines in the world. Today it is assumed that the deep biosphere is a largely unexplored habitat on earth and contains a considerable part of our planet's biomass in the form of microorganisms. As a rule, these microorganisms are likely to grow only slowly because the underlying redox processes provide little energy. The most unusual thing about the lithotrophic way of life of endolithic organisms is that they are the only organisms that can do without solar energy. Many are able to grow autotrophically, i.e. to bind carbon dioxide from their environment and to build up organic matter from purely inorganic compounds only with the help of chemical energy. Theoretically, such organisms could also exist on other celestial bodies .

The transition from endolithic organisms to soil organisms is often fluid. The isolation and characterization of endoliths is often difficult because they only occur in low cell densities, grow slowly and have very specific requirements for their environment, for example with regard to temperature , pH value, mineral composition and oxygen concentration .

See also

Web links