Deep-sea bacteria are microorganisms that thrive in the extreme conditions of the ocean's depths, often found at depths greater than 200 meters. These bacteria play a crucial role in the marine ecosystem by breaking down organic matter and recycling nutrients, which supports the food web in these dark environments. They can survive high pressure, low temperatures, and complete darkness, adapting to their unique surroundings. Many deep-sea bacteria are extremophiles, meaning they can withstand harsh conditions that would be lethal to most life forms. Some species are involved in chemosynthesis, using chemicals like hydrogen sulfide from hydrothermal vents to produce energy. This process is vital for sustaining life in areas where sunlight cannot reach, highlighting the importance of deep-sea bacteria in understanding marine biology and ecosystem dynamics.