Anoxygenic refers to a type of photosynthesis that does not produce oxygen as a byproduct. This process is primarily carried out by certain bacteria, such as purple sulfur bacteria and green sulfur bacteria. Instead of using water as an electron donor, these organisms typically utilize compounds like hydrogen sulfide or organic molecules. In contrast to oxygenic photosynthesis, which is performed by plants and cyanobacteria and releases oxygen, anoxygenic photosynthesis is often found in environments with low light and limited oxygen, such as deep water or mud. This adaptation allows these bacteria to thrive in unique ecological niches.