Green sulfur bacteria are a group of photosynthetic microorganisms that primarily thrive in anaerobic environments, such as deep-sea hydrothermal vents and sulfur-rich hot springs. They use light energy to convert carbon dioxide into organic compounds, relying on sulfur compounds instead of water for their photosynthesis. This process produces sulfur as a byproduct. These bacteria contain unique pigments called bacteriochlorophylls, which allow them to capture light energy efficiently in low-light conditions. Green sulfur bacteria play a crucial role in their ecosystems by contributing to the sulfur cycle and supporting the food web in their habitats, making them important for ecological balance.