A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye).

Microorganisms are often illustrated using single-celled, or unicellular organisms; however, some unicellular protists are visible to the naked eye, and some multicellular species are microscopic..

For more information about the topic Microorganism, read the full article at Wikipedia.org, or see the following related articles:

Prokaryote — Prokaryotes are organisms without a cell nucleus, or indeed any other membrane-bound organelles, in most cases unicellular (in rare cases, ...  > read more

Protozoa — Protozoa are single-celled eukaryotes (organisms whose cells have nuclei) that commonly show characteristics usually associated with animals, most ...  > read more

Yeast — Yeasts constitute a group of single-celled (unicellular) fungi, a few species of which are commonly used to leaven bread, ferment alcoholic ...  > read more

Organelle — In cell biology, an organelle is one of several structures with specialized functions, suspended in the cytoplasm of a eukaryotic cell. Eukaryotes ...  > read more

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A microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye).

The study of microorganisms is called microbiology.

Microorganisms include bacteria, fungi, archaea or protists, but not viruses and prions, which are generally classified as non-living.

Most microorganisms are single-celled, or unicellular, but some are microscopic, and some unicellular protists are visible to the average human. Microorganisms live almost everywhere on Earth where there is liquid water, including hot springs, on the ocean floor, and deep inside rocks within Earth's crust.

Microorganisms are critical to nutrient recycling in ecosystems as they act as decomposers.

As some microorganisms can also fix nitrogen, they are an important part of the nitrogen cycle.

However, pathogenic microbes can invade other organisms and cause diseases that kill millions of people every year. Microorganisms can be found almost anywhere in the taxonomic organization of life on the planet.

Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists and a number of fungi.

Viruses are generally regarded as not living and therefore are not microbes, although the field of microbiology also encompasses the study of viruses. Habitats and ecology Microorganisms are found in almost every habitat present in nature.

Even in hostile environments such as the poles, deserts, geysers, rocks, and the deep sea, some types of microorganisms have adapted to the extreme conditions and sustained colonies; these organisms are known as extremophiles.

Extremophiles have been isolated from rocks as much as 7 kilometres below the earth's surface, and it has been suggested that the amount of living organisms below the earth's surface may be comparable with the amount of life on or above the surface.

Extremophiles have been known to survive for a prolonged time in a vacuum, and can be highly resistant to radiation, which may even allow them to survive in space.

Many types of microorganisms have intimate symbiotic relationships with other larger organisms; some of which are mutually beneficial (mutualism), while others can be damaging to the host organism (parasitism).

If microorganisms can cause disease in a host they are known as pathogens. Microorganisms are vital to humans and the environment, as they participate in the Earth's element cycles such as the carbon cycle and nitrogen cycle, as well as fulfilling other vital roles in virtually all ecosystems, such as recycling other organisms' dead remains and waste products through decomposition.

Microbes also have an important place in most higher-order multicellular organisms as symbionts. Microorganisms are the cause of many infectious diseases.

The organisms involved include bacteria, causing diseases such as plague, tuberculosis and anthrax; protozoa, causing diseases such as malaria, sleeping sickness and toxoplasmosis; and also fungi causing diseases such as ringworm, candidiasis or histoplasmosis.

However, other diseases such as influenza, yellow fever or AIDS are caused by viruses, which are not living organisms and are not therefore microorganisms.

As of 2007, no clear examples of archaean pathogens are known, although a relationship has been proposed between the presence of some methanogens and human periodontal disease..

For more information about the topic Microorganism, read the full article at Wikipedia.org, or see the following related articles:

Prokaryote — Prokaryotes are organisms without a cell nucleus, or indeed any other membrane-bound organelles, in most cases unicellular (in rare cases, ...  > read more

Protist — Protists are a heterogeneous group of living things, comprising those eukaryotes that are neither animals, plants, nor fungi. They are usually ...  > read more

Soil life — Soil life is a collective term for all the organisms living within the soil. In a balanced soil, plants grow in an active and vibrant environment. ...  > read more

Infectious disease — In medicine, infectious disease or communicable disease is disease caused by a biological agent such as by a virus, bacterium or parasite. This is ...  > read more

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Marine Bacterium Suspected To Play Role In Global Carbon And Nitrogen Cycles (September 25, 2005) — Scientists are now revisiting, and perhaps revising, their thinking about how Archaea, an ancient kingdom of single-celled microorganisms, are involved in maintaining the global balance of nitrogen ...  > read more

Researchers Find Size Affects Growth Of Microorganisms In Mars-Like Environment (May 24, 2000) — When growing microorganisms under some Mars-like conditions, size does matter — at least if you’re talking about the sample size and surface area involved, according to two University of ...  > read more

NASA Scientist Discovers New Species Of Organism In Mars-like Environment (July 31, 2003) — They thrive without oxygen, growing in salty, alkaline conditions, and may offer insights into what kinds of life might survive on Mars. They're a new species of organism, isolated by scientists ...  > read more

Life In The Inferno: Researchers Identify Factors That Determine Where Microorganisms Can Survive In The Hellish World Deep Underground (December 22, 1999) — Subsurface scientists have begun to identify the factors that determine why microorganisms survive deep underground in some places, but not others, report researchers from the Department of ...  > read more

Bacteria Grown In Simulated Martian Environment (June 15, 1999) — A University of Arkansas researcher has become the first scientist to grow methane-producing microorganisms under some of the conditions found on Mars. His work may provide clues for finding similar ...  > read more

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