Anaerobic bacteria are microorganisms that thrive in environments without oxygen. They can be found in various places, such as deep soil, marshes, and the intestines of animals, including humans. These bacteria play essential roles in processes like decomposition and nutrient cycling. Unlike aerobic bacteria, which require oxygen to survive, anaerobic bacteria obtain energy through fermentation or other chemical processes. Some anaerobic bacteria are beneficial, aiding digestion and producing vitamins, while others can cause infections or diseases, such as Clostridium tetani, which leads to tetanus.