What is the Difference Between Obligate Aerobes and Obligate Anaerobes?

The main difference between obligate aerobes and obligate anaerobes lies in their oxygen requirements for growth and survival.

• Obligate aerobes are organisms that require a sufficient amount of oxygen for growth and survival. They depend on aerobic respiration and use oxygen as a terminal electron acceptor, meaning they cannot grow without oxygen. Examples of obligate aerobes include Mycobacterium tuberculosis.
• Obligate anaerobes are organisms that cannot grow in the presence of oxygen and may be killed by average atmospheric concentrations of oxygen. They depend on anaerobic respiration and fermentation, using a final electron acceptor other than oxygen. Obligate anaerobes usually lack enzymes such as catalase and superoxide dismutase, which are used by aerobic organisms to protect against oxygen radicals.

In summary:

• Obligate aerobes require oxygen for growth and survival, while obligate anaerobes require oxygen-free conditions to live and may be killed by the presence of oxygen.

There are other types of microorganisms with varying oxygen requirements, such as:

• Facultative anaerobes: can perform aerobic respiration if oxygen is present, but can also switch to anaerobic respiration if oxygen is not available.
• Aerotolerant anaerobes: do not require oxygen for growth, but can survive in the presence of oxygen without being harmed.
• Microaerophiles: require low concentrations of oxygen for growth, typically around 1%–10%, well below the 21% found in the atmosphere.

These different types of organisms can be identified by growing them in test tubes with varying oxygen concentrations, such as thioglycolate broth, an enriched, differential medium used primarily to determine the oxygen requirements of microorganisms.

Comparative Table: Obligate Aerobes vs Obligate Anaerobes

Here is a table summarizing the differences between obligate aerobes and obligate anaerobes:

Obligate aerobes require oxygen for growth and survival, while obligate anaerobes cannot grow in the presence of oxygen. Obligate aerobes depend on aerobic respiration, using oxygen as a terminal electron acceptor, and produce more energy compared to obligate anaerobes, which rely on anaerobic respiration. Examples of obligate aerobes include Mycobacterium tuberculosis, Nocardia, and Bacillus, while examples of obligate anaerobes are Clostridium, Bacteroides, and Propionibacterium. In a culture test tube, obligate aerobes grow close to the surface, while obligate anaerobes grow further away from the surface.