Bacterioplankton

Due to their boom and bust population dynamics and the enormous biomasses they can attain, jellyfish and ctenophores can have a large influence on the cycling of carbon (C), nitrogen (N) and phosphorus (P). This review initially summarises the biochemical composition of jellyfish, and compares and contrasts the mechanisms by which non-zooxanthellate and zooxanthellate jellyfish acquire and recycle C, N

The purpose of this paper was to assess the influence of basic limnological variables on bacterioplankton abundance in twenty lagoons in the Upper Paraná River floodplain, Brazil. Twelve abiotic (depth, total nitrogen, total phosphorus, dissolved organic carbon (DOC), water transparency, temperature, dissolved oxygen, alkalinity, pH, turbidity, electrical conductivity and total inorganic carbon), and two biotic (chlorophyll-a and rotifers abundance) limnological factors were used as independent variables to explain bacterial countings. Principal component analysis (PCA) was used to reduce the dimensionality of the abiotic data and chlorophyll-a. Subsequently, multiple regression analysis was used to examine the relationship between bacterial abundance and the principal component axes and rotifer densities. Bacterioplankton abundance fluctuated from 1.8 to 5.9 × 106 cells.ml−1 during the high water phase and from 1.4 to 4.0 × 106 cells.ml−1 during the low water phase and they were significantly higher during the former phase (t=3.06; p=0.007). Bacterial abundance was not significantly correlated with chlorophyll-a and rotifers abundance. On the other hand, it was positively correlated with principal components 1 and 2, indicating that DOC, total nitrogen and phosphorus concentration, temperature and pH are important to explain bacteria abundance. These results indicate that the input of different sources of DOC and inorganic nutrients from the floodplain into the lagoons during the high water phase is more important to explain bacterial abundance than autochthonous phytoplanktonic organic matter or predation by rotifers.

In high-nutrient low-chlorophyll areas, bacterial degradation of organic matter may be iron-limited. The response of heterotrophic bacteria to Fe addition may be directly controlled by Fe availability and/or indirectly controlled through the effect of enhanced phytoplankton productivity and the subsequent supply of organic matter suitable for bacteria. In the present study, the role of Fe on bacterial carbon degradation was investigated through regrowth experiments by monitoring bacterial response to organic substrates derived from Phaeocystis antarctica cultures set up in P. antarctica and on the quality of Phaeocystis-derived organic matter. Fe addition leaded to a decrease of C/N ratio of Phaeocystis material. The bacterial community composition was modified as observed from denaturing gradient gel electrophoresis (DGGE) profiles in LFe as compared to HFe bioassays. The percentage of active bacteria as well as their specific metabolic activities (ectoenzymatic hydrolysis, growth rates and bacterial growth efficiency) were enhanced in HFe bioassays. As a consequence, the lability of Phaeocystis-derived organic matter was altered, i.e., after seven days more than 90% was degraded in HFe and only 9% (dissolved) and 55% (total) organic carbon were degraded in LFe bioassays. By inducing increased bacterial degradation and preventing the accumulation of dissolved organic carbon, the positive effect of Fe supply on the carbon biological pump may partly be counteracted.

Aim: Microbial communities play a central role in environmental process such as organic matter mineralization and the nutrient cycling process in aquatic ecosystems. Despite their ecological importance, variability of the structure of archaeal and bacterial communities in freshwater remains understudied. Methods: In the present study we investigated the richness and density of archaea and bacteria in the water column and sediments of the Itupararanga Reservoir. We also evaluated the relationship between the communities and the biotic and abiotic characteristics. Samples were taken at five depths in the water column next to the dam and three depths next to the reservoir entrance. Results: PCR-DGGE evaluation of the archaeal and bacterial communities showed that both were present in the water column, even in oxygenated conditions. Conclusions: The density of the bacteria (qPCR) was greater than that of the archaea, a result of the higher metabolic plasticity of bacteria compared with archaea.

We studied the effects of the Prestige oil spill on Ría de Vigo bacterial abundance, production and community structure by using mesocosms (ca. 3500 l) filled with water from the center of the Ría, to which we added a realistic concentration of polycyclic aromatic hydrocarbons (PAHs; initial concentrations of approximately 20 to 30 μg l–1 chrysene equivalents) at each of the 4 periods of the seasonal cycle: spring bloom, summer stratification, autumn upwelling and winter. We followed the changes in bacterial activity by leucine and thymidine incorporation, and the changes in bacterial assemblage structure by 16S rDNA DGGE. In addition, simultaneously with the winter mesocosm experiment, we ran microcosms with fuel additions equivalent to 0.5, 1, 2 and 4× the treatment imposed on the mesocosms in the seasonal experiments. Bacterial community structure was also analyzed by CARD-FISH. We detected significant effects of the PAHs on bacterial community structure (increased number of bands) and production only in the summer experiment. In the microcosm experiments, we found similar effects to those in the mesocosms at PAH concentrations of ca. 20 to 40 μg l–1, and clear detrimental effects on phytoplankton at concentrations of ca. 80 μg l–1, with large development of Gammaproteobacteria. Our results indicate that an oil spill of the Prestige’s magnitude will have effects on the microbial resident community only at certain times of the year, while at higher PAH concentrations the effects might be more evident. For most of the year, the resident Ría de Vigo microbial communities appear to be accustomed to PAH concentrations such as those used in these experiments.

We present an improvement of the INT [2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride)] reduction method using Cyto-Clear slides, the fluorochrome DAPI (4(prm1),6(prm1)-diamidino-2 phenylindole), and an image analysis system. With this method we were able to simultaneously measure cell dimensions and formazan crystals as indicators of the respiratory activity of single bacteria. The method was tested on a natural bacterioplankton community of an oligotrophic high mountain lake (Gossenkollesee, Tyrolean Alps, Austria, 2,417 m above sea level) in midwinter ((symbl)1-m-thick ice and snow layer; dissolved organic carbon, 0.51 mg liter(sup-1); water temperature, 2(deg)C). About 25% of planktonic bacteria were respiratorily active, and a complex pattern of bacterial morphologies and specific respiratory activities was observed during a time series of INT incubation. Rod-shaped bacteria with cell lengths of between 1.6 and 4.8 (mu)m already showed visible activity after 0.5...

Seasonal shifts in bacterioplankton community composition in Toolik Lake, a tundra lake on the North Slope of Alaska, were related to shifts in the source (terrestrial versus phytoplankton) and lability of dissolved organic matter (DOM). A shift in community composition, measured by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes, occurred at 4°C in near-surface waters beneath seasonal ice and snow cover in spring. This shift was associated with an annual peak in bacterial productivity ([ 14 C]leucine incorporation) driven by the large influx of labile terrestrial DOM associated with snow meltwater. A second shift occurred after the flux of terrestrial DOM had ended in early summer as ice left the lake and as the phytoplankton community developed. Bacterioplankton communities were composed of persistent populations present throughout the year and transient populations that appeared and disappeared. Most of the transient populations could be divided into those that w...