PicocyanobacteriaPicocyanobacteria are cyanobacteria that are part of the picoplankton, which is the fraction of plankton composed by cells between 0.2 and 2 μm. Picocyanobacteria comprise the smallest photoautotrophs.GeneraFreshwater picocyanobacteria genera include Synechococcus, Cyanobium, and Synechocystis, and marine picocyanobacteria genera are represented primarily by Synechococcus and Prochlorococcus.