Question

Contrast an aerotolerant and an obligate anaerobe in terms of sensitivity to \(\mathrm{O}_{2}\) and ability to grow in the presence of \(\mathrm{O}_{2}\). How does an aerotolerant anaerobe differ from a microaerophile? (Section 5.16)

Short answer

Aerotolerant anaerobes tolerate \text{O}_2 and can grow with or without it, whereas obligate anaerobes cannot tolerate \text{O}_2 and only grow without it. Aerotolerant anaerobes do not need \text{O}_2, while microaerophiles require low \text{O}_2 (2-10%).

Step-by-step solution

Understanding Aerotolerant Anaerobes

Aerotolerant anaerobes do not require oxygen for growth, but they can tolerate its presence. They grow equally well whether oxygen is present or not.

Understanding Obligate Anaerobes

Obligate anaerobes are extremely sensitive to oxygen and cannot grow in its presence. Exposure to oxygen can be lethal for these organisms.

Aerotolerant Anaerobe vs. Microaerophile

Aerotolerant anaerobes differ from microaerophiles because microaerophiles require oxygen to grow, but at much lower concentrations than are present in the atmosphere. Microaerophiles grow best in environments with 2-10% oxygen, much lower than the 20% typically found in the atmosphere.

Sensitivity to \text{O}_2

Aerotolerant anaerobes are not sensitive to oxygen and can survive in its presence. In contrast, obligate anaerobes are highly sensitive to oxygen and cannot survive in its presence.

Growth in the Presence of \text{O}_2

Aerotolerant anaerobes can grow in both the presence and absence of oxygen. Obligate anaerobes cannot grow in the presence of oxygen and will only thrive in anaerobic (oxygen-free) environments.

Key concepts

oxygen sensitivity in microorganisms

Oxygen sensitivity in microorganisms can be quite diverse, impacting their ability to grow and survive. Some bacteria can thrive in environments with high oxygen levels, while others find oxygen to be lethal.

• Aerotolerant Anaerobes: These organisms do not need oxygen to grow, but unlike other anaerobes, they can tolerate its presence. This means they aren't harmed by oxygen and can survive in different environments.


• Obligate Anaerobes: In contrast, obligate anaerobes are extremely sensitive to oxygen. Oxygen exposure can damage their cellular structures, often leading to cell death. These microorganisms can only grow in environments completely void of oxygen.

Understanding this sensitivity to oxygen is crucial, especially when cultivating microorganisms in a lab setting or studying environmental samples. Identifying whether a microbe is an aerotolerant or an obligate anaerobe helps in determining the suitable conditions for its growth.

anaerobic growth

Anaerobic growth refers to the ability of microorganisms to thrive in environments without oxygen. Different bacteria have adapted unique strategies to grow anaerobically.

• Aerotolerant Anaerobes: These microbes can grow in both the absence and presence of oxygen. They are versatile because they ferment substrates to derive energy, regardless of oxygen availability.


• Obligate Anaerobes: These organisms rely solely on anaerobic processes to generate energy. When exposed to oxygen, the toxic by-products hinder their metabolic activities, making growth impossible in aerobic conditions.

Anaerobic growth is important in natural and engineered environments. For instance, in deep-sea vents or the human gut, anaerobic microorganisms play essential roles in maintaining ecological balance and health.

microaerophile characteristics

Microaerophiles are unique microorganisms that occupy a niche between strictly aerobic and anaerobic conditions. They require oxygen to grow but only in small amounts. Often, microaerophiles thrive in environments with oxygen concentrations ranging from 2-10%, much lower than the 20% found in our atmosphere. This specific oxygen need distinguishes them from both aerotolerant anaerobes and obligate anaerobes.

• Unlike aerotolerant anaerobes, which can grow equally well in both oxygen's presence and absence, microaerophiles perform poorly at higher oxygen levels and may even be harmed by them.


• Compared to obligate anaerobes, which cannot tolerate any oxygen, microaerophiles have evolved mechanisms to handle limited oxygen levels effectively. These organisms have specialized enzymes that detoxify reactive oxygen species (ROS).

Understanding microaerophile characteristics is crucial for microbiology and biotechnological applications. Culturing microaerophiles requires creating specific conditions that mimic their natural environments, ensuring optimal growth and survival.