A deep-sea bacterium is an anaerobe, meaning it does not require oxygen to survive. It is a type of microorganism that lives in the depths of the ocean, where oxygen levels are very low. Deep-sea bacteria are adapted to living in extreme environments and can be found in hydrothermal vents, cold seeps, and other deep-sea habitats. They play an important role in the global carbon cycle and are essential for the health of the ocean.