Anoxygenic photosynthetic bacteria are a group of microorganisms that can produce energy through photosynthesis without releasing oxygen. They use light energy to convert carbon compounds into organic matter, relying on pigments like bacteriochlorophyll. These bacteria thrive in environments where light is available but oxygen is scarce, such as in hot springs or deep-sea vents. Unlike oxygenic photosynthetic organisms like plants and cyanobacteria, anoxygenic bacteria do not use water as an electron donor. Instead, they may utilize substances like hydrogen sulfide or organic compounds. This unique process allows them to occupy ecological niches where oxygenic photosynthesis cannot occur.