Cyanobacteria
Cyanobacteria form oxygen during photosynthesis. It is thought that it was these bacteria that were responsible for the first appearance of significant amounts of oxygen on earth about 2.3 billion years ago.
Today, many different forms and shapes of Cyanobacteria are known. In environmental samples Cyanobacteria are easily recognized by light microscopy. If illuminated with green light, they will show a bright red auto fluorescence. This is due to the presence of phycobili proteins and chlorophyll a.