What is Cyanobacteria or Blue-green bacteria?

Blue-green bacteria, or cyanobacteria, used to be classified as blue-green algae within the Plant Kingdom, primarily because they have the same green photosynthetic pigment chlorophyll a as plants, as well as similar photosynthetic processes.

However, cyanobacteria have accessory photosynthetic pigments that differ from those present in plants. Cyanobacteria accessory pigments, which give them their distinctive blue-green color, are soluble in water, while plant accessory pigments are not. These special types of water-soluble pigments are called phycobilins, and are found in only two other groups - red algae and the cryptomonads.

Microscopic cyanobacteria cells vary in their life styles. Some live as solitary single cells, some as multicellular organisms, while some live together as colonies. Cyanobacteria are found in almost every environment on Earth, from underneath Arctic ice to hot springs that reach temperatures of up to 98.8 degrees C (210 F). They are often the pioneer inhabitants of bare volcanic rock, and can be found in almost any aquatic habitat. They also live symbiotically with fungi as lichens.

Cyanobacteria are very important organisms ecologically speaking. They are given credit for producing the oxygen that was originally absent from the primitive Earth's atmosphere. Certain species of cyanobacteria also produce toxins that cause rashes called swimmers' itch. Cyanobacteria sometimes produce "blooms" in ponds and lakes, which are indicative of polluted conditions. Cyanobacteria play the very important role of "fixing" atmospheric nitrogen, making it available for use in the food web.