Biogeochemical controls on the bacterial populations in the eastern Atlantic Ocean

Abstract

Abstract.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, particulateCorrespondence to: R. J. Lara (ruben.lara@zmt-bremen.de) organic C [POC] and N [PON]). Instead, we found a highly significant correlation between bacterial abundance and temperature (p < 0.001) and a significant correlation with DOC and DON (p < 0.005 and < 0.01, respectively). In comparison to CBC and DAPI-stained prokaryotes, cultivable Vibrio showed a stronger and highly significant correlation with DOC and DON (p < 0.0005 and p < 0.005, respectively). In cold waters of the mesopelagic and abyssal zones, CBC was 50 to 100-times lower than in the surface layer; however, cultivable Vibrio spp. could be isolated from the bathypelagic zone and even near the seafloor (average ∼10 CFU l −1 ). The depth-wise decrease in CBC and Vibrio coincided with the decrease in both DOC and POC. Our study indicates that Vibrio and other bacteria may largely depend on dissolved organic matter to survive in nutrient-poor oceanic habitats.

Effect of Climate Change on the Concentration and Associated Risks ofVibrioSpp. in Dutch Recreational Waters

“…The empirical formula for Vibrio spp. derived here shows a temperature effect that is the same as was derived for the Atlantic Ocean by Neogi et al . Other formulas from the literature (Table ) did not show any correspondence.…”

“…As reviewed previously, quantitative predictions on future Vibrio concentrations in recreational waters are lacking . In the literature, several empirical relations between Vibrio presence or concentration and environmental factors have been described . Table gives an overview of empirical relations between the concentration of Vibrio spp.…”

“…Although the effects of these parameters are highly species dependent, in general, temperature and salinity are considered most important. (6)(7)(8)(9)(10)(11) Other parameters include nutrient and chlorophyll-a concentrations and pH. (10,12,13) Climate change is expected to both directly and indirectly affect these environmental conditions.…”

Dynamics of dissolved organic carbon in eutrophic Lake Taihu and its tributaries and their implications for bacterial abundance during autumn and winter

“…Thus, elucidating the relationships between DOC dynamics and BA is a significant ecological issue. Temperature is among the most important ecological parameters affecting phytoplankton composition, bacterial growth, and biological activity (White et al 1991;Kobari et al 2010;Neogi et al 2011). Bacterial abundances in our study were within the range reported by Zhu et al (2009) in their study of Lake Taihu.…”

“…Previous studies have reported that BA is controlled by DOC concentration (Naganuma & Seki 1993;Neogi et al 2011) and that bacteria can rapidly utilize DOC of autochthonous origin (Chen & Wangersky 1996). However, the interaction between DOC and BA is complex, as the interaction can be affected by other factors, such as photodegradation of DOC (Lindell et al 1995;Catal an et al 2013) and bacteria loss due to sedimentation and grazing (Work & Havens 2003;Tang et al 2010).…”