What does anaerobe mean?
An anaerobe is any organism — usually a microorganism such as a bacterium or archaeon — that can live and grow without molecular oxygen. The term covers a spectrum: obligate (or strict) anaerobes are not merely indifferent to oxygen but poisoned by even trace amounts, while facultative anaerobes can switch between oxygen-dependent and oxygen-free metabolism depending on conditions. Anaerobes occupy ecological niches where air cannot reach, from deep-sea sediments and waterlogged soils to the human gut and infected wounds. The word is chiefly scientific, appearing in microbiology, medicine, food safety, and environmental science; everyday readers more often meet its adjective form, as in 'anaerobic digestion' or 'anaerobic exercise'. Its counterpart is the aerobe, an organism that depends on oxygen. Because many medically important bacteria — including Clostridium species responsible for tetanus and botulism — are anaerobes, the word carries practical weight well beyond the laboratory.
nounAn organism, especially a microorganism, that can live and grow without oxygen; some anaerobes are actually harmed or killed by its presence.
- A microorganism that grows without free oxygen; in the strict sense (obligate anaerobe), one for which oxygen is lethal.
- More loosely, any organism able to survive or function in oxygen-free conditions, including facultative organisms that tolerate both.
"Clostridium botulinum is an anaerobe that thrives in sealed, oxygen-free environments such as improperly canned food."
"Deep layers of lake sediment are dominated by anaerobes, which decompose organic matter without oxygen."
"The lab cultured the wound sample under nitrogen because the suspected pathogen was a strict anaerobe."
Regular plural; commonly used when referring to groups or communities of such organisms.
"Obligate anaerobes were isolated from the deep sediment cores."
Some anaerobes aren't just indifferent to oxygen — it's literally poisonous to them, making Earth's most abundant gas a deadly toxin.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of anaerobe
The noun 'anaerobe' was formed in the late nineteenth century from Greek roots: the prefix 'an-' meaning 'without', 'aēr' meaning 'air', and 'bios' meaning 'life'. It arose alongside the adjective 'anaerobic' after Louis Pasteur's work demonstrated that fermentation could proceed without free oxygen. The same elements underlie related terms such as 'aerobe', 'aerobic', and 'anaerobiosis'.
Related word forms
How anaerobe is actually used
Primarily a technical term used in microbiology, medicine, and environmental science; in general prose the adjective 'anaerobic' (as in 'anaerobic exercise') is far more common than the noun. In precise scientific use, 'anaerobe' is often qualified as 'obligate', 'strict', or 'facultative' depending on the organism's tolerance of oxygen.
Easily confused with anaerobe
An aerobe requires oxygen to live and grow, whereas an anaerobe lives without it — and obligate anaerobes are killed by exposure to oxygen.