The term aerotolerant anaerobe refers to an organism that A) does not use oxygen but tolerates it. B) is killed by oxygen tolerates normal atmospheric nitrogen gas levels. D) requires less oxygen than is present in air. E) requires more oxygen than is present in air
The Correct Answer and Explanation is:
Correct Answer: A) does not use oxygen but tolerates it.
Explanation
An aerotolerant anaerobe is a type of microorganism that does not use oxygen for its metabolic processes, but unlike obligate anaerobes, it is not harmed by the presence of oxygen. These organisms rely entirely on fermentation or anaerobic respiration to generate energy, and they do so regardless of the availability of oxygen.
To understand this better, it’s useful to place aerotolerant anaerobes within the context of other microbial oxygen classifications:
- Obligate aerobes require oxygen to survive, as they use aerobic respiration.
- Facultative anaerobes can use oxygen when it’s present but can switch to anaerobic metabolism if oxygen is absent.
- Obligate anaerobes cannot survive in the presence of oxygen.
- Microaerophiles need oxygen, but only at lower concentrations than atmospheric levels.
- Aerotolerant anaerobes, on the other hand, are indifferent to the presence of oxygen. They neither use it nor are poisoned by it.
An example of an aerotolerant anaerobe is Streptococcus pyogenes, a bacterium responsible for diseases such as strep throat. This organism carries out fermentation regardless of oxygen availability and continues producing lactic acid from glucose whether oxygen is present or not.
Aerotolerant anaerobes often possess enzymes like superoxide dismutase (SOD) and peroxidase, which detoxify reactive oxygen species such as superoxide radicals and hydrogen peroxide. This enables them to survive in oxygenated environments, unlike strict anaerobes that lack these protective enzymes and are therefore damaged by oxygen exposure.
In microbiology labs, the oxygen tolerance of organisms is often tested using thioglycollate broth, which creates a gradient of oxygen concentration. Aerotolerant anaerobes typically grow uniformly throughout the medium, showing they do not depend on oxygen nor are inhibited by it.
Thus, the key characteristic of aerotolerant anaerobes is their ability to tolerate but not utilize oxygen, making option A the correct answer.
