Biogeochemical controls on the bacterial population in the eastern Atlantic Ocean.

NEOGI, S.B.; KOCH, B.P.; SCHMITT-KOPPLIN, P.; POHL, C., ; KATTNER, G.; YAMASAKI, S. ; LARA, R.J.

BIOGEOSCIENCES

COPERNICUS PUBLICATIONS

Lugar: Gottingen; Año: 2011 vol. 8 p. 3747 - 3759

1726-4170

Little is known about bacterial dynamics in theoligotrophic ocean, particularly about cultivable bacteria. Weexamined the abundance of total and cultivable bacteria in relationto changes in biogeochemical conditions in the easternAtlantic Ocean with special regard to Vibrio spp., a groupof 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 Nand 24 S. Chlorophyll-a was very low (<0.3 μg l−1) in mostareas of the nutrient-poor Atlantic, except at a few locationsnear upwelling regions. In surface water, dissolved organiccarbon (DOC) and nitrogen (DON) concentrations were 64?95μMC and 2?10μM N accounting for 90% and 76%of total organic C and N, respectively. DOC and DON graduallydecreased to 45μMC and <5μMN in the bottomwater. In the surface layer, culture independent total bacteriaand other prokaryotes represented by 40-6-diamidino-2-phenylindole (DAPI) counts, ranged mostly between 107and 108 cells l−1, while cultivable bacterial counts (CBC)and Vibrio spp. were found at concentrations of 104?107and 102?105 colony forming units (CFU) l−1, respectively.Most bacteria (>99 %) were found in the nanoplankton fraction(<20 μm), however, bacterial abundance did not correlatewith suspended particulates (chlorophyll-a, particulateorganic C [POC] and N [PON]). Instead, we found a highlysignificant correlation between bacterial abundance and temperature(p <0.001) and a significant correlation with DOCand DON (p <0.005 and <0.01, respectively). In comparisonto CBC and DAPI-stained prokaryotes, cultivable Vibrioshowed a stronger and highly significant correlation withDOC and DON (p <0.0005 and p <0.005, respectively). Incold waters of the mesopelagic and abyssal zones, CBC was50 to 100-times lower than in the surface layer; however, cultivableVibrio spp. could be isolated from the bathypelagiczone and even near the seafloor (average 10 CFU l−1). Thedepth-wise decrease in CBC and Vibrio coincided with thedecrease in both DOC and POC. Our study indicates thatVibrio and other bacteria may largely depend on dissolvedorganic matter to survive in nutrient-poor oceanic habitats.