A microorganism or microbe is an organism that is so small that it is invisible to the naked eye. The term is synonymous by usage to single-celleded organism, even though some unicellular protists are visible to the naked eye, and some colonial species are microscopic.
Microorganisms may be found almost anywhere in the taxonomic structure. Bacteria and archaea are always or almost always microscopic, as are most protists. Even some fungi, a primarily macroscopic taxon, are microorganisms.
Microorganisms are found everywhere in nature, owing to the existence of extremophiles, microorganisms that have adapted to generally hostile environments. Extremophiles may be found in environments such as the poles, deserts, geysers, just beneath the surface of rockss, and the bottom of the deep sea. Some are known to survive prolonged time in vacuum, or to be unusually resistant to radiation.
Microorganisms can be helpful in recycling other organisms' remains and waste products, or when employed in biotechnology, e.g., for brewing and bakery. They can also be harmful as pathogens when, as parasites, causing infections.
- BBC News, 28 September, 2001: The microbes that 'rule the world' Citat: "... The Earth's climate may be dependent upon microbes that eat rock beneath the sea floor, according to new research....The number of the worm-like tracks in the rocks diminishes with depth; at 300 metres (985 feet) below the sea floor, they become much rarer..."
- BBC News, 10 July, 2000, Snow microbes found at South Pole Citat: "...able to survive the large doses of ultraviolet radiation, extreme cold and darkness...The microbes have DNA sequences similar to a category of bacteria known as Deinococcus..."
- BBCNews: 16 January, 2002, Tough bugs point to life on Mars Citat: "...This research demonstrates that certain microbes can thrive in the absence of sunlight by using hydrogen gas..."
- BBCNews: 17 January, 2002, Alien life could be like Antarctic bugs