Which type of bacteria is completely dependent on fermentation, even in the presence of oxygen?

The type of bacteria that is completely dependent on fermentation, even in the presence of oxygen, falls under aerotolerant anaerobes. These organisms are unique because they do not utilize aerobic respiration and instead rely solely on fermentation processes for energy production regardless of the presence of oxygen.

Aerotolerant anaerobes can tolerate oxygen but do not use it for growth; they can survive in oxygen-rich environments but do not derive any metabolic benefit from the presence of oxygen. This distinguishes them from other types of anaerobes, such as obligate anaerobes, which are harmed by oxygen, and facultative anaerobes, which can use oxygen when available but can also switch to fermentation under anaerobic conditions. Microaerophiles also require limited levels of oxygen for growth but do not depend exclusively on fermentation like aerotolerant anaerobes do.

Understanding these metabolic pathways helps illustrate the versatility and diversity of bacteria and their adaptations to various environmental conditions.