Variations in pelagic bacterial communities in the North Atlantic Ocean coincide with water bodies

Abstract

Physical and chemical characteristics define oceanographic regions. The potential for a distinct biogeography of bacterial communities in these oceanic provinces was studied in epi- pelagic and upper mesopelagic water bodies of the North Atlantic Ocean by terminal restriction fragment length polymorphism (T-RFLP) analysis of bacterial 16S rRNA genes and flow cytome- try. Water samples from 67° N to 34° N along the 30° W meridian contained epipelagic populations of Synechococcus in the north and Prochlorococcus in the south. Bacterial communities were gen- erally more diverse in phototrophic layers above the pycnocline. Communities significantly dif- fered in the epipelagic zone along the latitudinal transect through the different oceanic provinces and between the epipelagic and the upper mesopelagic zone. Differences in the T-RFLP patterns coincided well with differences in the physico-chemical conditions of the sampling sites. Changes in bacterial communities were traced to characteristic terminal restriction fragments (TRFs). In sil- ico assignments of phylogenetic groups to TRFs, e.g. populations of high-light and low-light eco- types of Prochlorococcus, supported our T-RFLP analysis of bacterial communities. Distinct bacte- rial communities in water bodies of the North Atlantic Ocean hosted different bacterial populations, which may serve as biological markers for oceanic provinces.