Pelagibacter communis

Pelagibacter communis, written Candidatus Pelagibacter communis, is a small marine bacterium of the SAR11 clade in the class Alphaproteobacteria. It was isolated in 2002 and given a provisional name, although it has not been formally described under the bacteriological code. It is probably among the most abundant organisms in the ocean and perhaps in the whole world, making up about a quarter of all microbial plankton cells and around half the cells in temperate surface water in summer. The cells are rod or crescent shaped, among the smallest self-replicating cells known, and the strain HTCC1062 has the smallest genome of any free-living organism, with about 1.3 million base pairs and 1,354 open reading frames. It recycles dissolved organic carbon, carries proteorhodopsin genes that power a light driven proton pump, and can be grown on a defined medium with reduced sulfur, glycine, pyruvate and vitamins. A population can double about every 29 hours.