Oceans prokaryotes

Giovannoni, S. J., and M. Rappe. 2000. Evolution, diversity, and molecular ecology of marine prokaryotes. In Microbial Ecology of the Oceans (D. Kirchman, Ed.)., Wiley Sons, New York. 

The term bacteria in the ocean is commonly used to describe prokaryotes (Archaea and Bacteria). In the last 20 years, there has been an explosion in the understanding of the phylogeny of bacteria that is based primarily upon culture-independent sequencing of the universally conserved genes (i.e., those on which there is strong evolutionary selection) involved in ribosome function (Giovannoni and Rappe, 2000 Olsen et al. 

Chisholm S. W., Olson R. J., Zettler E. R., Goericke R., Waterbury J. B., and Welschmeyer N. A. (1988) A novel free-living prokaryote abundant in the oceanic euphoric zone. Nature 334, 340-343. 

Within this diverse group of organisms, three basic evolutionary lineages are discernable (Delwiche, 2000). The first contains all prokaryotic oxygenic phytoplankton, which belong to one class of bacteria, namely, the cyanobacteria. Cyanobacteria are the only known oxygenic photoautotrophs that existed prior to —2.5 Gyr BP (Ga) (Lipps, 1993 Summons et al., 1999). These prokaryotes numerically dominate the photoautotrophic community in contemporary marine ecosystems and their continued success bespeaks an extraordinary adaptive capacity. At any moment in time, there are —10 cyanobacterial cells in the contemporary oceans. To put that into perspective, the number of cyanobacterial cells in the oceans is two orders of magnitude more than all the stars in the sky. 

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