How Do Aerobic and Anaerobic Bacteria Impact Humans and the Environment?
Anaerobic bacteria are microorganisms that survive in the absence of oxygen. They cannot tolerate oxygen at all and will die if exposed to an environment that has a high quantity of oxygen. Anaerobic metabolism involves organic or inorganic redox reactions, fermentation reactions and anaerobic reaction which produces highly volatile fatty acids and gaseous molecules such as methane and alcohol.
Anaerobic Bacteria can be Classified Into:
Facultative Anaerobes: These anaerobes are the most versatile and they preferentially utilize oxygen as a terminal electron acceptor. They can also metabolize in the absence of oxygen by reducing other compounds. Much more usable energy, in the form of high-energy phosphate, is obtained when a molecule of glucose is completely catabolized to CO2 and H2O in the presence of O2 (38 molecules of ATP) than when it is only partially catabolized by a fermentative process in the absence of O2 (2 molecules of ATP).
Microaerophilic Anaerobes: These types of anaerobes can only proliferate in low concentrations of oxygen (2 to 10%) or in an atmosphere with high CO2 concentration i.e. 10% of CO2.
Obligate Anaerobes: Obligate anaerobes are completely incapable of aerobic metabolism but they are variably tolerant to oxygen. These organisms can be categorized into three different classes. These are:
Strict: Tolerance level of only ≤ 0.5% of Oxygen
Moderate: Tolerance level of 2-8 % of Oxygen
Aero Tolerant Anaerobes: These obligate anaerobes can tolerate atmospheric oxygen for a limited time. These anaerobic bacteria require oxygen to live.
Anaerobic Bacteria Examples
Bacteroides, Bifidobacterium, Fusobacterium, Porphyromonas, Prevotella, Actinomyces,
Propionibacterium, Clostridia, etc are the examples of such bacteria. Anaerobic bacteria are medically significant as they cause many infections in the human body. For example, various species of Clostridia can cause food poisoning, soft-tissue infection, etc, whereas Actinomyces can cause head, neck, abdominal and pelvic infections.
What are Aerobic Bacteria?
As the name suggests, aerobic bacteria come under the class of microorganisms which grow and survive in an oxygenated environment, in short, aerobic bacteria require oxygen to live. Aerobic bacteria are critical for biological decomposition. The presence of oxygen hastens the decomposition of hydrocarbons. This type of decomposition can be seen on the forest floor, where aerobes are decomposing leaves and other organic debris. Organic material decomposition is an aerobic process. As the amount of carbon dioxide in the atmosphere rises, the rate of decomposition slows. Surprisingly, aerobic composting does not produce a foul odour. It's critical to know what the anaerobic process is before proceeding. A process that takes place in the presence of oxygen is known as an aerobic process.
Aerobic Bacteria can be Classified Into:
Obligate Aerobes: Obligate aerobes need oxygen to survive. "organisms that require oxygen to thrive and survive." So, in biology, obligatory aerobes are creatures that can only grow and survive in the presence of oxygen since they get their energy through aerobic respiration with oxygen. The process of oxidative phosphorylation in oxidative (aerobic) respiration, which uses oxygen as the terminal electron acceptor, provides energy to these organisms.
They utilize atmospheric oxygen to oxidize substrates such as sugar and fats to generate energy and carry out metabolic activities. Aerobic microorganisms use glycolysis, the Krebs TCA cycle, and an electron transport chain with oxygen as the final electron acceptor. The enzymes used are catalase, peroxidase, and superoxide dismutase.
Facultative Aerobes: The aerobes use oxygen when it is available but are not solely reliant on it. They have anaerobic methods of energy production.
Microaerophiles: They require oxygen for energy production. However, a high concentration of atmospheric oxygen is harmful to them. They use fermentation reactions for energy and do not have an electron transport system.
Aerotolerant Aerobes: They do not use oxygen for metabolic activities and are not harmed by it. They lack all three enzymes needed to break down oxygen.
Aerobic Bacteria Examples: Some examples of aerobic bacteria are Nocardia sp. Pseudomonas aeruginosa, E. Coli, Citrobacter, Klebsiella, Proteus, Salmonella, Achromobacter Mycobacterium tuberculosis etc.
Differentiate Between Aerobic and Anaerobic Bacteria
In this section, we will discuss the differences between aerobic and anaerobic bacteria.
Aerobic and Anaerobic Bacteria List:
Aerobic Bacteria List:
E. Coli
Citrobacter
Klebsiella
Proteus
Salmonella
Achromobacter
Anaerobic Bacteria List:
Actinomyces
Bifidobacterium
Fusobacterium
Propionibacterium
Clostridium
Bacteroides
Prevotella
FAQs on Aerobic vs Anaerobic Bacteria: Differences, Examples & Uses
1. What is the primary difference between aerobic and anaerobic bacteria?
The primary difference lies in their relationship with oxygen. Aerobic bacteria require oxygen to survive and carry out cellular respiration, using it as the final electron acceptor to generate energy. In contrast, anaerobic bacteria do not require oxygen and may even be harmed or killed by its presence. They use other molecules, like sulfates or nitrates, as their final electron acceptor in an alternative energy-producing pathway.
2. What are some common examples of aerobic and anaerobic bacteria?
Here are some common examples of each type:
- Aerobic Bacteria: Mycobacterium tuberculosis (causes tuberculosis), Pseudomonas aeruginosa (can cause infections in hospitals), Bacillus species, and Nocardia.
- Anaerobic Bacteria: Clostridium botulinum (causes botulism), Clostridium tetani (causes tetanus), and Bacteroides fragilis (part of the normal gut flora but can cause infections if displaced).
3. How are bacteria classified based on their relationship with oxygen?
Bacteria are classified into several groups based on their oxygen requirements:
- Obligate Aerobes: Absolutely require oxygen for growth and survival.
- Obligate Anaerobes: Oxygen is toxic to them; they can only grow in oxygen-free environments.
- Facultative Anaerobes: Can grow with or without oxygen. They prefer using oxygen for aerobic respiration because it yields more energy, but can switch to anaerobic respiration or fermentation if oxygen is absent.
- Aerotolerant Anaerobes: Do not use oxygen for growth but can tolerate its presence without being harmed.
- Microaerophiles: Require low concentrations of oxygen for growth, as normal atmospheric levels are toxic to them.
4. Why is oxygen toxic to obligate anaerobic bacteria?
Oxygen is toxic to obligate anaerobes because they lack the necessary enzymes to neutralise harmful byproducts of oxygen metabolism. When oxygen is present, it can form reactive oxygen species (ROS) like superoxide radicals and hydrogen peroxide. Aerobic and facultative organisms produce enzymes like superoxide dismutase (SOD) and catalase to break down these toxic substances. Obligate anaerobes do not have these protective enzymes, leading to cellular damage and death upon exposure to oxygen.
5. How does the classification of bacteria as aerobic or anaerobic relate to aerobic and anaerobic respiration?
This classification is directly linked to the type of respiration the bacteria perform. Aerobic bacteria perform aerobic respiration, a metabolic process that uses oxygen as the final electron acceptor to efficiently produce a large amount of ATP (energy). Anaerobic bacteria perform anaerobic respiration, which uses a different molecule (not oxygen), such as nitrate, sulfate, or carbon dioxide, as the final electron acceptor. This process yields less energy than aerobic respiration. Therefore, the bacterial type is defined by the metabolic pathway it uses for energy production.
6. How do facultative anaerobes provide a survival advantage compared to obligate types?
Facultative anaerobes have a significant survival advantage due to their metabolic flexibility. Unlike obligate aerobes, which die without oxygen, and obligate anaerobes, which die in its presence, facultative anaerobes can thrive in a wide range of environments. They can efficiently generate energy using oxygen when it's available and can switch to less efficient anaerobic pathways to survive when oxygen is scarce. This adaptability allows them to colonise diverse habitats, such as the human gut, soil, and water.
7. What is the clinical importance of identifying bacteria as aerobic or anaerobic?
Identifying whether an infection is caused by aerobic or anaerobic bacteria is crucial for diagnosis and treatment. For example:
- Specimen Collection: Anaerobic bacteria die in air, so special oxygen-free transport media are needed to culture them from a patient sample.
- Treatment Strategy: Aerobic bacteria like Staphylococcus aureus often cause skin and soft tissue infections. Anaerobic infections, like those caused by Clostridium, often occur in deep wounds or internal abscesses and may produce gas and tissue-destroying toxins. The choice of antibiotics and treatment approach depends heavily on this classification.
