Nostoc cyanobacteria. Darkfield illuminated light micrograph of a spherical colony of filamentous Nostoc sp. cyanobacteria (bright lines). Cyanobacteria are bacteria that obtain their energy through photosynthesis. Nostoc have the ability to fix atmospheric nitrogen, thereby playing a major role in soil fertility. They have a wide distribution and are commonly found in soil and on mud, rocks and plants. Magnification: x71 when printed 10 centimetres wide.