microorganism

American  

[mahy-kroh-awr-guh-niz-uhm] / ˌmaɪ kroʊˈɔr gəˌnɪz əm /

noun

• microorganisms
  plural

1. any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae.

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microorganism British  

/ ˌmaɪkrəʊˈɔːɡəˌnɪzəm /

noun

1. any organism, such as a bacterium, protozoan, or virus, of microscopic size

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microorganism Scientific  

/ mī′krō-ôr′gə-nĭz′əm /

1. An organism that can be seen only with the aid of a microscope and that typically consists of only a single cell. Microorganisms include bacteria, protozoans, and certain algae and fungi.

2. See Note at germ

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Other Word Forms

Derived Forms

• microorganic
  adjective
• microorganismal
  adjective

Inflected Forms

Nouns

• microorganisms
  plural

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Etymology

Origin of microorganism

First recorded in 1875–80; micro- + organism

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Explanation

A microorganism is a living thing that is too small to see with the naked eye. Bacteria and amoebas are microorganisms, and while not technically "alive," viruses are also considered microorganisms. The only way to see a microorganism is through a microscope, an instrument used to magnify images of very small things. Microorganisms are fundamental to life on Earth. They decompose dead things, recycle nutrients, aid in digestion, and strengthen our immune systems. They are a key part of biotechnology: Microorganisms are used to treat sewage, clean up pollution, and create medicines. Microorganisms are also used in making foods like bread and cheese. On the negative side, a few microorganisms are harmful, as they can cause disease. Another word for microorganism is microbe.

Example Sentences

See Examples For:

microorganism microorganisms

Yet this everyday microorganism may also offer insight into a far bigger question: how life might endure the extreme conditions found beyond Earth.

From Science Daily ● Feb. 8, 2026

“The presence of terrestrial microorganism within a sample of Ryugu underlines that microorganisms are the world's greatest colonizers and adept at circumventing contamination controls,” the authors conclude.

From Salon ● Nov. 24, 2024

Unlike bacteria, the microorganism is less likely to exchange genetic material with other microbes and doesn't take up residence in the gastrointestinal tract where it could potentially disrupt microbial communities.

From Science Daily ● Nov. 20, 2024

Mr. Gutman is the founder of Primer’s Yeast, a company that sells ancient strains of the microorganism.

From New York Times ● Jun. 20, 2024

The disease is caused by a microorganism and several bacteria have been suspected of being responsible.

From Special Report on Diseases of the Horse by Charles B. Michener

The discovery also raises a broader question about how rapidly microorganisms can adapt to synthetic materials introduced into their environment.

From Science Daily ● Oct. 16, 2026

Most conventional plastics break down extremely slowly because microorganisms struggle to digest the synthetic polymers from which they are made.

From Science Daily ● Oct. 16, 2026

For microorganisms to make a meaningful difference in reducing plastic pollution, more plastic products would need to be made from biodegradable materials that contain chemical bonds microbes can break apart.

From Science Daily ● Oct. 16, 2026

One possibility that deserves closer examination is disruption of the gut microbiome, the community of microorganisms living in the digestive system.

From Science Daily ● Oct. 14, 2026

To test this question, many years ago my colleagues and I prepared chambers that simulated the Martian environment as it was then known, inoculated them with terrestrial microorganisms and waited to see if anybody survived.

From "Cosmos" by Carl Sagan

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Related Words

• bacterium
• microbe
• pathogen
• virus

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