Bacteria are typically single-celled organisms called prokaryotes that may serve as digestive aids, cause disease or aid in decomposition. Unlike eukaryotes, they do not have nuclei. Bacteria contain their DNA and other genetic material as a single strand in their cytoplasm, and they reproduce through a process called binary fission.
Bacteria can thrive in hot and cold environments. Psychrophiles are bacteria that prefer colder environments, while thermophiles thrive in hot environments. Extreme thermophiles can live around extremely hot hydrothermal vents on the ocean floor.
Bacteria that live in an organism's digestive system can help break down tough food material for easier digestion. These types of bacteria also serve an essential role as waste decomposers.