The SAR11 clade dominates ocean surface bacterioplankton communities

On average SAR11 accounts for a third of the cells present in surface waters and nearly a fifth of the cells present in the mesopelagic zone. In some regions members of the SAR11 clade represent as much as 50% of the total surface microbial community and 25% of the sub-euphotic microbial community. It is estimated that globally there are 2.4x10^28 SAR11 cells in the oceans, half of which are located in the euphotic zone. This suggests that this microbial group is among the most successful organisms on Earth – even though the biogeochemical role of the SAR11 clade is unknown.