Prochlorococcus is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation (chlorophyll a2 and b2). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth. Prochlorococcus microbes are among the major primary producers in the ocean, responsible for a large percentage of the photosynthetic production of oxygen.^[1][2] Prochlorococcus strains, called ecotypes, have physiological differences enabling them to exploit different ecological niches.^[3] Analysis of the genome sequences of Prochlorococcus strains show that 1,273^[4] genes are common to all strains, and the average genome size is about 2,000 genes.^[1] In contrast, eukaryotic algae have over 10,000 genes.^[4]

The genus and the type species were made validly published names under the ICNP in 2001 with Validation list no. 79.^[5] They became valid under the ICNafp in 2020 with the description of Komárek et al.^[6]

(From Wikipedia, June 2025)