Microbial sphere. Coloured scanning electron micrograph (SEM) close-up of filaments (green) of cyanobacteria on the surface of a microbial sphere. A microbial sphere is a symbiosis between several microscopic marine organisms found in the North Sea. At first, the sphere consists of bacteria and diatoms, then cyanobacteria grow in and on the sphere. The sphere falls apart after a few weeks. The spheres studied so far consist of Phormidium cyanobacteria, Navicula diatoms and heterotrophic bacteria. Magnification: x1850 when printed 10cm wide.