Obligate anaerobes are microorganisms that cannot survive in the presence of oxygen. They rely on anaerobic processes, such as fermentation or anaerobic respiration, to generate energy. These organisms are often found in environments like deep soil, sediments, and the intestines of animals, where oxygen levels are low or nonexistent. Due to their inability to tolerate oxygen, obligate anaerobes can be sensitive to changes in their environment. Some species, such as Clostridium and Bacteroides, play important roles in processes like digestion and nutrient cycling. Understanding obligate anaerobes is crucial for fields like microbiology and medicine.