Which Types of Bacteria Thrive in Environments That Lack Free Oxygen?
Though animals require oxygen to survive, there are bacteria that can live without it. In fact, many bacteria are harmed by the presence of oxygen. Bacteria that do not need oxygen are called anaerobic bacteria. Anaerobic bacteria are ancient organisms, older than organisms requiring oxygen. Some anaerobic bacteria live in the guts of animals, which is an arrangement beneficial to both parties. If they escape the gut, however, and enter other tissues it is very dangerous for the host.
