What is the definition of facultative bacteria?

Facultative bacteria are defined by their ability to adapt to varying oxygen levels in their environment. This means they can survive in both aerobic (with oxygen) and anaerobic (without oxygen) conditions. This versatility allows them to switch their metabolic processes depending on the availability of oxygen; they can utilize aerobic respiration when oxygen is present or switch to fermentation or anaerobic respiration when it is not.

For instance, many bacteria in the gut are facultative and can thrive regardless of whether oxygen is available. They play important roles in various ecological processes and biogeochemical cycles, showcasing their adaptability. This adaptability is crucial in numerous environments, including human microbiomes and natural ecosystems. Understanding facultative bacteria is essential in fields such as microbiology, environmental science, and medicine.