Cyanobacteria, or cyaneans, or blue algae or chlorophyll.
Their photosynthesis, like plant photosynthesis, produces oxygen dioxide that uses sulphur instead of water.
Today cyanobacteria live everywhere, in the ocean, in freshwater, and on land, they can live in symbiosis with other organisms, and plant cell chlorplas, organellas in which photosynthesis takes place, are thought to be descendants of cyanobacteria symbiotes.
In water and soil, they convert nitrogen from air to ammonium and nitrates that can be used by plants and are thus fertilizer.
Risk of cyanobacteria
Cyanobacteria can become hazardous to fauna and flora when they breed in the environment during algae blooms, and they emit cyanotoxins, sometimes fatal to animals and dangerous to humans.