Facultative anaerobe
Overview
A facultative anaerobe is a type of microorganism that can survive in both oxygen-rich and oxygen-deprived environments. Unlike obligate anaerobes, which can only survive in environments devoid of oxygen, or obligate aerobes, which require oxygen for survival, facultative anaerobes are capable of adjusting their metabolic processes to suit the oxygen availability in their environment.
Metabolism
Facultative anaerobes are unique in their metabolic flexibility. They can switch between aerobic respiration and anaerobic respiration or fermentation, depending on the oxygen levels in their environment.
During aerobic respiration, oxygen is used as the final electron acceptor in the electron transport chain, resulting in the production of water and energy in the form of ATP. This is the most efficient way of generating energy and is preferred when oxygen is available.
In the absence of oxygen, facultative anaerobes switch to anaerobic respiration or fermentation. In anaerobic respiration, an inorganic substance other than oxygen, such as nitrate or sulfate, is used as the final electron acceptor. In fermentation, an organic substance, typically a derivative of the substrate, acts as the final electron acceptor.
Examples
Many species of bacteria, such as Escherichia coli and Staphylococcus aureus, are facultative anaerobes. These bacteria are commonly found in the human gut and skin, respectively, where they can survive in both oxygen-rich and oxygen-deprived conditions.
Some types of yeast, such as Saccharomyces cerevisiae, the yeast used in baking and brewing, are also facultative anaerobes. They can switch between aerobic respiration and fermentation, depending on the oxygen levels in their environment.
Significance in Medicine
Facultative anaerobes play a significant role in medicine, particularly in the field of infectious diseases. Many pathogenic bacteria are facultative anaerobes, which allows them to survive and proliferate in various parts of the human body, including oxygen-rich areas like the lungs and oxygen-deprived areas like the gut.
The ability of these bacteria to switch between metabolic processes also has implications for antibiotic treatment. Some antibiotics target specific metabolic pathways, and the metabolic flexibility of facultative anaerobes can make them more resistant to these treatments.
Significance in Biotechnology
In the field of biotechnology, facultative anaerobes are used in various industrial processes. For example, Saccharomyces cerevisiae is used in the baking and brewing industries. In the presence of oxygen, it undergoes aerobic respiration, but when oxygen is depleted, it switches to fermentation, producing ethanol and carbon dioxide, which are essential for beer brewing and bread making.
Facultative anaerobes are also used in the treatment of wastewater. They can degrade organic pollutants in both aerobic and anaerobic conditions, making them valuable in the biological treatment processes of wastewater treatment plants.