Facultative Aerobes: Definition & Examples

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  • 0:02 Facultative Anaerobic Bacteria
  • 0:49 The Importance of Oxygen
  • 1:48 Examples
  • 3:38 Lesson Summary
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Lesson Transcript
Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Facultative anaerobic bacteria stand out from other bacteria because they can live with or without oxygen. Some of these anaerobes can also cause disease in humans.

Facultative Anaerobic Bacteria

Before we start describing facultative anaerobic bacteria, we should go over what the words 'aerobic' and 'anaerobic' mean. Aerobic means there is oxygen available to use. For example, when you are doing aerobic exercise, your heart is actively working to get oxygen to your cells. Anaerobic means an environment without oxygen.

Bacteria can be classified based on how they use oxygen. Obligate aerobes are obligated to use oxygen, meaning they have to have oxygen in the environment in order to survive. Obligate anaerobes do not require oxygen, and many cannot even live in the presence of oxygen. Facultative anaerobes are the most versatile type of bacteria -- they can live either with or without oxygen.

The Importance of Oxygen

Oxygen is important for respiration, which is how cells, like bacteria, turn food energy into a form of energy they can easily use. This usable energy is called adenosine triphosphate, or ATP for short. ATP is like currency that the cell can spend readily to do work. Food must first be converted to ATP, just like your paycheck must first be converted to cash before you can go shopping.

Facultative anaerobes grow best with oxygen. Aerobic respiration is very efficient at producing ATP, so this is ideal. However, when oxygen is unavailable, facultative anaerobes can still survive and grow -- just not as well. Anaerobic respiration is much less efficient. With oxygen, bacteria can make up to 38 molecules of ATP. Without oxygen, the bacteria can only make about 2 molecules of ATP. So, even though they are surviving, facultative anaerobes don't grow as quickly in environments without oxygen.


There are many different facultative anaerobes, but the most interesting from a health standpoint are pathogens, or microbes that cause disease. Bacteria species including Salmonella species, Shigella, and Escherichia coli (E. coli) are the most familiar examples of facultative anaerobes. All of these bacteria are associated with infection of the digestive system.

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