Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
An obligate anaerobe is a microorganism that cannot survive in the presence of oxygen. It obtains energy through anaerobic processes like fermentation or anaerobic respiration.
5 Must Know Facts For Your Next Test
Obligate anaerobes are killed by atmospheric levels of oxygen (21%).
They typically thrive in environments such as deep soil, sediments, and the gastrointestinal tract.
Common genera include Clostridium and Bacteroides.
These organisms utilize alternative electron acceptors like nitrate or sulfate during respiration.
The presence of superoxide dismutase and catalase enzymes is usually minimal or absent in obligate anaerobes.
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Related terms
Facultative Anaerobe: A bacterium that can grow with or without oxygen.
Microaerophile: A microorganism that requires low levels of oxygen for growth but is damaged by higher concentrations.
Aerotolerant Anaerobe: An organism that does not use oxygen but can tolerate its presence.