Microorganisms in the soil
In all layers of the ground, microorganisms are diverse and abundant. They feed off dead organic material that they cut into fine particles, making the material easily assimilated by all types of plants. As the decomposers of organic waste and the agents of demineralisation, microorganisms are responsible for the cycling of matter on Earth.
Microorganisms of the deep
Soils are characterized by layers of variable thickness and structure. Each layer differs from the preceding and following ones in colour, texture, structure, porosity, pH, and organic and mineral content. These distinct characteristics then influence the humidity, as well as the gaseous and biological contents of the different layers of soil. A layer rich in organic matter, where great biological activity exists, is quite different from a stone layer with little organic content and therefore little biological activity.
Bacteria live thousands of metres under the surface of the earth, in the underground petroleum reservoirs. Some bacteria use gaseous hydrogen as an energy source as well as the carbon from carbon dioxide, even though it is inorganic. These bacteria excrete simple organic compounds that are in turn consumed by other bacteria. These microorganisms can live indefinitely without carbon from the surface, since the essential nutrients are constantly renewed in their environment.
In rock formations where energy sources and food are rare, bacteria have adapted by shrinking in size from a few microns to less than one micron. By using their reserves during periods of deprivation, they have permanently slowed down their metabolism. Their cell division occurs only once per century or less, whereas bacteria on the surface reproduce within a few minutes, a few hours, or at most a few months.
The role of microorganisms in recycling
Microorganisms play a key role in preserving life on Earth by acting as a link between animals and plants. Responsible for numerous transformations, they convert dead animals and plants into simple inorganic substances that feed the plants, which in turn will become food for animals. Microorganisms are indispensable for many essential biochemical processes that result in recycling elements such as sulphur, nitrogen, and carbon.