Which bacteria type cannot tolerate oxygen at all?

The type of bacteria that cannot tolerate oxygen at all is obligate anaerobes. These bacteria thrive in environments devoid of oxygen and are harmed or even killed when exposed to it. This intolerance is due to the absence of the necessary enzymes, such as superoxide dismutase and catalase, that would allow them to neutralize reactive oxygen species that can be generated in the presence of oxygen.

Facultative anaerobes, on the other hand, can survive in both the presence and absence of oxygen, often using oxygen for energy production when it is available. Obligate aerobes require oxygen for their metabolic processes and cannot survive without it. Aerobic bacteria, which include obligate aerobes, also need oxygen to grow and perform cellular respiration. Therefore, they are similar in function and are not examples of bacteria that cannot tolerate oxygen.

In contrast, the strict requirements of obligate anaerobes for an oxygen-free environment set them apart as the only type that cannot survive any exposure to oxygen.