Biogeochemical controls on bacteria in the Atlantic Ocean (original) (raw)

Little is known about bacterial dynamics in the oligotrophic ocean, particularly about cultivable bacteria. We examined the abundance of total and cultivable bacteria in relation to changes in biogeochemical conditions in the eastern Atlantic Ocean with special regard to Vibrio spp., a group of bacteria that can cause diseases in human and aquatic organisms. Surface, deep water and plankton (<20 µm, 20-55 µm and >55 µm) samples were collected between 50 • N and 24 • S. Chlorophyll-a was very low (<0.3 µg l −1 ) in most areas of the nutrient-poor Atlantic, except at a few locations near upwelling regions. In surface water, dissolved organic carbon (DOC) and nitrogen (DON) concentrations were 64-95 µM C and 2-10 µM N accounting for ≥90 % and ≥76 % of total organic C and N, respectively. DOC and DON gradually decreased to ∼45 µM C and <5 µM N in the bottom water. In the surface layer, culture independent total bacteria and other prokaryotes represented by 4 -6-diamidino-2-phenylindole (DAPI) counts, ranged mostly between 10 7 and 10 8 cells l −1 , while cultivable bacterial counts (CBC) and Vibrio spp. were found at concentrations of 10 4 -10 7 and 10 2 -10 5 colony forming units (CFU) l −1 , respectively. Most bacteria (>99 %) were found in the nanoplankton fraction (<20 µm), however, bacterial abundance did not correlate with suspended particulates (chlorophyll-a, particulate