Anaerobic organism
organism living in the absence of oxygen
An anaerobic organism or anaerobe is an organism that does not require molecular oxygen for growth or energy metabolism. Anaerobes produce adenosine triphosphate (ATP) by fermentation, anaerobic respiration, or both. During anaerobic respiration, substances other than oxygen serve as the terminal electron acceptor.
Anaerobes are commonly classified according to their relationship with oxygen. Obligate anaerobes are harmed by it. Aerotolerant organisms do not use oxygen but can tolerate it, whereas facultative anaerobes can grow without oxygen but use it when available.
Most anaerobes are microorganisms, including bacteria, archaea, protozoa, and fungi, although a small number of anaerobic multicellular animals are known. Anaerobes occur in oxygen-depleted environments and in symbiotic associations with other organisms. Culturing anaerobes often requires oxygen-free techniques.
First recorded observation
In his 14 June 1680 letter to the Royal Society, Antonie van Leeuwenhoek described an experiment he carried out by filling two identical glass tubes about halfway with crushed pepper powder, to which some clean rain water was added.
This brief starts where responsible research should: with the source description of “Anaerobic organism” as organism living in the absence of oxygen. Everything that follows is an evidence route, not borrowed authority.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Aug 23, 2026. The linked authority identifier is Q189790. The Library of Congress control number is sh85004755. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank. The first chronological checks are 1680.
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This entry incorporates text from “Anaerobic organism” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.