What is the main characteristic of obligate anaerobes?

Obligate anaerobes are microorganisms that cannot survive in the presence of oxygen. Their metabolism is adapted to environments devoid of oxygen, and exposure to oxygen can lead to cellular damage or death. This is because obligate anaerobes often lack the necessary enzymes, such as superoxide dismutase and catalase, to neutralize toxic byproducts of oxygen, such as reactive oxygen species.

In contrast, those that thrive in high levels of oxygen, such as aerobic organisms, have mechanisms to utilize oxygen for energy production safely. The option regarding survival in low oxygen environments pertains more to facultative anaerobes, which can utilize both aerobic and anaerobic pathways depending on the availability of oxygen. While binary fission is a common method of reproduction for many types of bacteria, including anaerobes, it is not a defining characteristic exclusive to obligate anaerobes, making this detail less relevant in identifying their primary trait.