Microorganisms are very small living organisms. They are microscopic and can be unicellular or multicellular (Madigan and Martinko 2006). Microorganisms include all prokaryotes and some eukaryotes. They are usually not visible to the naked eye, but some macroscopic ones can also be seen with the naked eye (Max Planck Society Research News, published September 15, 2012). Microorganisms include bacteria, archaea, protozoa, fungi, algae, and some members of the kingdom Animalia such as rotifers and planarians. Viruses also fall into this category, i.e. microorganisms, but some researchers even consider them non-living (Rybicki 1990) (LWOFF 1956). Microorganisms inhabit every sphere of planet Earth. They inhabit the most extreme environments where no other living organism can survive. Such microbes are known as “extremophiles”. These may include the following: a) Acidophiles: - these include those organisms which can survive in highly acidic conditions or with a very low pH which is generally less than 2. Acidophiles belong to all three classes: Archaea, Bacteria and Eukarya . Example: Acetobacter aceti, Dunaliella acidophila, Acidianus infernus etc.b) Basophiles: This class includes organisms that can thrive in extremely alkaline conditions with a pH above 10. These are also known as alkaliphiles. Example: Halorhodospira halocloris, Natromonas pharaonis, Thiohalospira alkaliphira etc.c) Thermophilic:- these are those organisms which thrive easily in very high temperatures like 45 degrees Celsius and up to 122 degrees Celsius. At such high temperatures no other living organism survives other than this certain class of microorganisms. Examples: Sulfobolus solfataricus, Sulfobolus acidocalda...... middle of paper ......tattributed to the fact that they are too expensive and the range of toxic materials they can decontaminate is very small. This led researchers to look for alternative solutions. This is how the use of microorganisms for bioremediation began. This use of microorganisms provides an environmentally friendly technique of remediating harmful substances without having any alternative effects that could disturb the homeostasis of the environment in any way. Many microorganisms live in the bodies of humans and other animals as well. The most common of these is the Lactobacillus bacterium found in the human mouth, intestines and vagina of women. Lactobacillus has the ability to bind to detoxify some of the most harmful radionuclides and toxic metals. Thanks to this property, Lactobacillus is now also used in packaged frozen foods and also in fermented preparations.