What kind of organisms grow only in the absence of oxygen?

The term for organisms that grow only in the absence of oxygen is anaerobes. These organisms rely on anaerobic processes for their energy production, using substances other than oxygen for respiration. This adaptation allows them to thrive in environments where oxygen is either absent or toxic to them. Anaerobes can be found in diverse environments, such as deep aquatic sediments, the intestines of animals, or in some industrial applications.

In contrast, aerobes are organisms that require oxygen for their growth and energy production, often using it in a process called aerobic respiration. Facultative anaerobes can grow in both the presence and absence of oxygen, meaning they can adapt to varying conditions, switching between aerobic and anaerobic respiration depending on the availability of oxygen. Microaerophiles are a specific group of organisms that require a low concentration of oxygen for their growth but cannot tolerate atmospheric levels of oxygen. Thus, recognizing the distinct definitions and roles of these categories clarifies why anaerobes specifically grow only in environments devoid of oxygen.