What type of bacteria can only grow in the absence of oxygen?

Obligate anaerobes are a specific type of bacteria that require an environment devoid of oxygen to survive and grow. This is due to their metabolic pathways, which do not utilize oxygen as a final electron acceptor in respiration. Instead, they rely on anaerobic respiration or fermentation processes that happen in the absence of oxygen.

These bacteria possess enzymes that can be harmful or inactive in the presence of oxygen, making aerobic conditions toxic to them. The inability to tolerate oxygen is a defining feature of obligate anaerobes, distinguishing them from other types of bacteria that can survive or thrive in varying oxygen concentrations. For instance, facultative anaerobes can grow with or without oxygen, and microaerophiles require low levels of oxygen to survive but still cannot tolerate atmospheric levels, while obligate aerobes need oxygen for their metabolic processes.