Cyanobakterium

Cyanobacteria, sometimes referred to as cyanobacteria in plural and cyanobacterium when speaking of a single organism, are a phylum of photosynthetic prokaryotes that conduct oxygenic photosynthesis. They are among the oldest known life forms on Earth and played a key role in shaping the planet’s atmosphere by releasing substantial amounts of oxygen. They are not true algae, despite the common name blue-green algae, and they display a wide range of forms and lifestyles.

Cyanobacteria vary from unicellular to multicellular and filamentous types, often forming colonies enveloped in mucilaginous sheaths. Some species differentiate specialized cells called heterocysts for nitrogen fixation, enabling them to convert atmospheric nitrogen into usable forms under certain conditions. Photosynthesis in cyanobacteria uses chlorophyll a and accessory pigments such as phycobiliproteins (phycocyanin, phycoerythrin, allophycocyanin), imparting diverse blue-green, green, or reddish colors. They inhabit a wide range of environments, including freshwater, marine systems, soils, deserts, hot springs, and even symbiotic associations with fungi, plants, and lichens.

Ecologically, cyanobacteria contribute primary production and nutrient cycling. They fix carbon dioxide and, in many species, nitrogen gas through specialized cells, supporting food webs in nutrient-poor habitats. However, some cyanobacterial blooms can proliferate under nutrient enrichment and warm conditions, producing toxins such as microcystins, cylindrospermopsins, and saxitoxins that threaten water quality and public health. Management of blooms and monitoring of toxins are important in water resources and ecosystem health.

Research and applications include studying ancient geology and evolution, exploring bioactive compounds, and developing biotechnologies for carbon capture, bioremediation, and sustainable production.