Microorganisms and Their Influence on Radionuclide Migration in Igneous Rock Environments

A microbe is an organism that has all it needs for a complete life cycle in one single cell. Many microbial species may under appropriate circumstances form multi-cellular structures, sometimes with morphological and metabolic differentiations between the different cells making up a bio-structure. Growth by cell division is the most common way of microbe propagation. The microbes outnumber multi-cellular organisms on our planet. They are characterised by their almost infinite ability to bio-degrade and bio-synthesize naturally occurring compounds in the environment. Microbial reactions control, partly or fully, the chemical composition of many, very different environments such as sediments, soils, lakes and groundwater. They also have the ability to adapt to extreme environments such as alkaline and acidic groundwater. 2 Microbes occur either as unattached, planktonic cells passively floating or actively swimming in the free water phase, or are attached to solid surfaces. Any solid surface, living or dead, immersed in a water phase with living microbes is predestined to develop biofilms i.e. films of life that cover the surface. Microbes from the water phase become attached to the surface and, if growth conditions are appropriate, they start to grow and divide, in an attached mode. All microbial life is based on metabolic processes driven by chemical energy extracted from the oxidation of inorganic or organic compounds. The oxidative harvesting of energy requires an electron acceptor that is concomitantly reduced. This process is called respiration when a reducible external electron acceptor is used (e.g. oxygen, nitrogen, sulphur, iron or manganese), and fermentation when the electrons are shuffled around between the degradation products of the original energy source (e.g. sugar to alcohol and carbon dioxide). The microbes certainly must obey the laws of thermodynamics, but they are utterly sophisticated lawyers that understand to use every single, constructive combination of those laws for making a good living of all or almost nothing.