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Cyanobacteria, often referred to as blue-green algae, are a group of photosynthetic microorganisms that belong to the domain Bacteria. They are among the oldest known life forms on Earth and have long played a significant role in Earth’s ecosystems. Cyanobacteria perform oxygenic photosynthesis, a process that produces oxygen as a byproduct, and contributed greatly to the Great Oxygenation Event.

Key characteristics of cyanobacteria include their ability to capture energy from sunlight through chlorophyll and other pigments, which they use to convert carbon dioxide and water into organic compounds while releasing oxygen. This process is crucial for the continued oxygenation of Earth’s atmosphere and the support of aerobic life forms (like humans).

Cyanobacteria are found in diverse environments, including freshwater, marine habitats, soils, and even extreme environments such as hot springs and deserts. They can occur as single cells or form colonies, filaments, or mats. These forms also include stromatolites. Some cyanobacteria have the ability to fix nitrogen from the atmosphere, making them important contributors to nitrogen cycles in ecosystems. While cyanobacteria provide various ecological benefits, some species can produce toxins under certain conditions, leading to harmful algal blooms in water bodies. These blooms can have detrimental effects on aquatic ecosystems and pose risks to human and animal health.