What type of organisms are considered facultative anaerobes?

Facultative anaerobes are organisms that have the ability to switch between aerobic and anaerobic metabolism based on the availability of oxygen in their environment. This means that they can utilize oxygen when it is present, allowing them to undergo aerobic respiration, which is generally more energy-efficient. However, when oxygen is scarce or absent, they can still generate energy through anaerobic processes, such as fermentation or anaerobic respiration. This versatility allows facultative anaerobes to thrive in a wide range of environments.

In contrast, other types of organisms have more restrictive metabolic needs. There are strict aerobes that require oxygen for survival and cannot grow without it, and strict anaerobes that can only survive in the absence of oxygen. Therefore, the definition of facultative anaerobes as those that can switch between metabolism types captures their unique adaptability and ecological significance.