Differential interference contrast (DIC) light micrograph of Spirulina meneghiniana cf. cyanobacteria filaments. Each filament is a colony of bacterial cells. Cyanobacteria are photosynthesising bacteria that are found in most habitats where water is present. They are also used as a health food and dietary supplement because of their high protein content. Magnification: x400 when printed at 10 centimetres wide.