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At least 235 records · Page 13Linked to original sources
PubMed1978

A plankton net designed to exclude air-sea interface phenomena.

For use in trace pollutant studies a description is presented of a protected closed plankton net whose purpose is to minimize the exposure of collected samples to surface films and debris. Tests described in this paper appeared to show that the protected closed net was not necessary for the environmental conditions encountered during our field studies. However, additional calculations based on the data of other investigators strongly imply that employment of such a net is heavily polluted surface waters may be highly advantageous.

Air↗
PubMed2004

Urovirulence of Pseudomonas aeruginosa: planktonic cells vs. biofilm cells.

Planktonic and biofilm cells of a clinical urinary isolate of P. aeruginosa were compared in vitro for their ability to adhere to uroepithelial cells, interaction with macrophages, and for production of virulence factors like extracellular proteinase, elastase, hemolysin, phospholipase C and pyochelin. Biofilm cells showed increased adherence to UECs, which was coupled with reduced uptake and intracellular killing by macrophages. Overall there was a decrease in production of extracellular products by biofilm cells. Comparing the two cell forms for their ability to establish infection in an ascending model of acute pyelonephritis, significant enhancement of renal bacterial load, as well as more pronounced renal pathology developed with biofilm cells.

Animals↗
PubMed2002

Large differences in the fraction of active bacteria in plankton, sediments, and biofilm.

Generally, only a small fraction of free-living pelagic bacteria are metabolically active, while particle-associated bacteria usually exhibit a larger proportion of active bacteria. Most previous studies on the active fraction of bacteria focus on planktonic communities, and there are only a few studies on sediment and epiphytic biofilm bacteria. We compared the active fraction of the total number of bacteria in three different habitats of the littoral zone of Lake Erken, Sweden, including the sediments, the epiphytic biofilm on the submerged macrophyte Ranunculus circinatus, and the water column. Active bacteria were detected as those with an active electron transport system, identified by the capacity to reduce the tetrazolium salt CTC (5-cyano-2,3-ditolyltetrazolium chloride) into its fluorescent, water insoluble state. There were large differences between habitats. The active fraction of the total number of bacteria detected by fluorescence microscopy (annual mean +/- SD) in the sediments was 46 +/- 10%, on R. circinatus 37 +/- 18%, and in the water column 4 +/- 4%. The abundance of CTC-reducing cells was correlated with total bacterial abundance, and the fraction of CTC-reducing bacteria generally increased with total bacterial abundance, for all the habitats. Consequently, the difference in the fraction of CTC-reducing bacteria between the habitats could be attributed to different densities of bacteria, with a larger proportion of active bacteria at higher bacterial densities.

Animals↗
PubMed1991

Stability patterns and trophic structure in a Delaware Bay plankton community.

Using qualitative loop analysis we have extended our examination of a Delaware Bay plankton community to include an investigation of the roles played by the various entities (population, guild or nutrient) in the community. In an entity removal exercise, we used stability relationships as a probe into community structure. Six types of stability change are possible as a result of entity removal from the system: stable to stable (s-->s); stable to unstable (s-->u); stable to disconnected (s-->d); unstable to stable (u-->s); unstable to unstable (u-->u); unstable to disconnected (u-->d). Using these changes as an investigative tool, we found that in order to account for the stability-instability patterns, it was necessary to construct a refined trophic structure model. The observed connections between the entities in the larger model could be grouped into two different types of stability substructures: a simple pattern and a more complex branching pattern. These patterns map easily onto the refined trophic structure model. Using stability analysis it is also possible to model community structure in ways other than the traditional trophic approach. Patterns of system necessity and relative contribution to stability are observed. These patterns match the refined trophic structure model derived previously. The roles that the various entities play in the overall community were followed over an annual cycle. Entities were seen to change their roles as a function of time and status within a subgroup. These results show that stability determinations have the potential to be used as a valuable tool in community analysis.

Animals↗
PubMedDate not supplied

[Enumeration and size of planktonic bacteria determined by image analysis coupled with epifluorescence].

The interest of the image analysis procedure is the time-saving in automated planktonic bacterial counting and sizing, with the possibility of manual visual field control at all times. Bacterial biomass (in number and volume) and bacterial projected area histograms were determined with a microcomputer. Performance limits of image-analysed epifluorescence microscopy were: camera sensitivity, considering the very low fluorescence levels on stained bacteria; pixel-micron conversion factor, and the impossibility of the apparatus distinguishing between bacteria and fluorescent small particles. This method is not of interest for counting sediment bacteria.

Animals↗
PubMed2004

Comparative proteomic analysis of planktonic and immobilized Pseudomonas aeruginosa cells: a multivariate statistical approach.

The protein maps of Pseudomonas aeruginosa cells from two natural (attached) and one artificial (gel-entrapped) immobilized-cell (IC) systems, together with their free (suspended) counterparts, were compared after incubation for 18 or 48 h in a minimal salt medium. Principal component analysis (PCA) was used to interpret the variations in protein spot densities that were observed on electropherogram obtained by two-dimensional electrophoresis (2-DE). PCA of the 2-DE data, a matrix of 933 rows (observations, i.e., spot density values) and 12 columns (variables, i.e., incubation conditions), in which observations were standardized horizontally, extracted four principal components (PCs) accounting for 78.75% of the variability in the protein expression profiles. PC1 opposed the two modes of growth (planktonic and immobilized) while PC2 discriminated between the incubation times of free cell cultures. The incubation conditions of ICs, including the immobilization procedure (entrapment vs attachment) and the nature of the biofilm substratum, were fairly separated in PC3xPC4. The dependence of the protein patterns on the cell immobilization process was further illustrated by the identification of a number of peptides whose amount remained unchanged or was altered in ICs compared to free bacteria. These results reinforce the topical assertion that bacteria in the immobilized state display a specific physiological behavior but also question the existence of a unique IC phenotype.

Bacterial Proteins↗
PubMed2004

The effects of mixotrophy on the stability and dynamics of a simple planktonic food web model.

Recognition of the microbial loop as an important part of aquatic ecosystems disrupted the notion of simple linear food chains. However, current research suggests that even the microbial loop paradigm is a gross simplification of microbial interactions due to the presence of mixotrophs-organisms that both photosynthesize and graze. We present a simple food web model with four trophic species, three of them arranged in a food chain (nutrients-autotrophs-herbivores) and the fourth as a mixotroph with links to both the nutrients and the autotrophs. This model is used to study the general implications of inclusion of the mixotrophic link in microbial food webs and the specific predictions for a parameterization that describes open ocean mixed layer plankton dynamics. The analysis indicates that the system parameters reside in a region of the parameter space where the dynamics converge to a stable equilibrium rather than displaying periodic or chaotic solutions. However, convergence requires weeks to months, suggesting that the system would never reach equilibrium in the ocean due to alteration of the physical forcing regime. Most importantly, the mixotrophic grazing link seems to stabilize the system in this region of the parameter space, particularly when nutrient recycling feedback loops are included.

Algorithms↗
PubMed2003

Description of a tandem repeated DNA sequence of Echinostoma caproni and methods for its detection in snail and plankton samples.

Echinostome larval stages in the snail have a great potential as effective competitors for the control of schistosomes and adult worms can cause painful intestinal diseases in humans. Ecology and transmission of the larval stages of trematodes are poorly understood, especially because their identification in field-collected samples by microscopy is difficult. We cloned, sequenced and analysed a 192 bp tandem repreated DNA sequence of Echinostoma caproni (EcSau3A), an often discussed antagonist of Schistosoma mansoni in Biomphalaria snails. PCR primers against this sequence can detect less than 10 fg of E. caproni DNA, 2 miracidia in snails 1 day p.i., 1 metacercaria in 50 mg snail tissue and 1 cercaria in 50 mg plankton with high specificity. Methods described in this study can support the discovery of fundamental ecological principles on distribution, host specificity and epidemiology of E. caproni larvae under field conditions.

Animals↗
PubMed2005

Detection and identification of spirolides in norwegian shellfish and plankton.

Mussels sampled in the spring of 2002 and 2003 from Skjer, a location in Sognefjord, Norway, tested positive in the mouse bioassay for lipophilic toxins. The symptoms, which included cramps, jumping, and short survival times (as low as 4 min), were not characteristic of toxins previously observed in Norway. A survey of the algae present at the aquaculture sites showed that the toxicity correlated with blooms of Alexandrium ostenfeldii. Up to 2200 cells/L were found at the peak of one bloom. In Canadian waters, this alga is known to be a producer of the cyclic imine toxins, spirolides. Analysis of mussel extracts from Skjer in the spring of 2002 and 2003, using liquid chromatography tandem mass spectrometry, revealed the presence of several new spirolides. The same compounds were also found in algal samples dominated by A. ostenfeldii, which had been sampled from Skjer in February 2003. A large-scale extraction of mussel digestive glands and chromatographic fractionation of the extracts allowed the isolation and structure elucidation of the main spirolide, 20-methyl spirolide G, with a molecular weight of 705.5. This is the first confirmed occurrence of spirolides in mussels and plankton from Norway.

Acetals↗
PubMed2002

Community structure and function in prokaryotic marine plankton.

Molecular biodiversity studies of microbial communities have provided invaluable information on the existence of heretofore unknown organisms and on community composition. Cloning and 'fingerprinting' techniques have been used many times to study prokaryote community composition of marine plankton. There are still many opportunities for new discoveries in this area, but the results have also opened new questions about the activities of these organisms and their function, going beyond just listing taxa or counting organisms. Rarely can the broad function be inferred from phylogenetic position alone (e.g. cyanobacteria). The recent discovery of abundant non-cyanobacterial marine phototrophs points to our inability to link phylogenetic position with function in a detailed way. One approach we have found fruitful is to combine fluorescence in situ hybridization with microautoradiography, a technique dubbed STARFISH. A recent application has shown that ubiquitous archaea from the deep sea, phylogenetically related to extreme thermophiles, are active in the uptake of amino acids from ambient (nanomolar) concentrations. This suggests the group is at least partly heterotrophic and able to compete successfully with bacteria for nutrients. Other as-yet uncultivated groups are also amenable to similar studies.

Animals↗
PubMed2001

Unexpected diversity of small eukaryotes in deep-sea Antarctic plankton.

Phylogenetic information from ribosomal RNA genes directly amplified from the environment changed our view of the biosphere, revealing an extraordinary diversity of previously undetected prokaryotic lineages. Using ribosomal RNA genes from marine picoplankton, several new groups of bacteria and archaea have been identified, some of which are abundant. Little is known, however, about the diversity of the smallest planktonic eukaryotes, and available information in general concerns the phytoplankton of the euphotic region. Here we recover eukaryotes in the size fraction 0.2-5 microm from the aphotic zone (250-3,000 m deep) in the Antarctic polar front. The most diverse and relatively abundant were two new groups of alveolate sequences, related to dinoflagellates that are found at all studied depths. These may be important components of the microbial community in the deep ocean. Their phylogenetic position suggests a radiation early in the evolution of alveolates.

Animals↗
PubMed1992

Novel major archaebacterial group from marine plankton.

Marine bacteria often dominate the plankton biomass and are responsible for much of the cycling of organic matter, but bacterial diversity is poorly understood because conventional identification methods (requiring culturing) miss about 99% of the organisms. Recent advances permit characterization of microbial communities by analysis of 16S ribosomal RNA gene sequences directly from biomass without the need to culture the organisms; such studies from surface ocean samples have found only eubacteria, not archaebacteria (or Archaea), which are profoundly different. Here we report 16S rRNA sequences obtained from Pacific Ocean bacterioplankton samples collected from depths of 100 m and 500 m. Among these we found sequences only distantly related to those of any organisms previously characterized by 16S rRNA sequences, with similarities to the nearest such relatives (extreme thermophiles) approximately the same as those between animals and plants. We suggest that these sequences are from a previously undescribed archaebacterial group that may have diverged from the ancestors of characterized organisms very early in evolution.

Animals↗
PubMed2003

Extracellular phosphatase activity of natural plankton studied with ELF97 phosphate: fluorescence quantification and labelling kinetics.

ELF(R)97 phosphate (ELFP) is a phosphatase substrate which produces ELF(R)97 alcohol (ELFA), a fluorescent water-insoluble product, upon hydrolysis. We studied the kinetics of ELFA precipitation in freshwater samples at levels of total plankton and single phytoplankton cells, and tested the suitability of ELFP for measurement of surface-bound algal extracellular phosphatases. Samples from acidic Plesné Lake (pH approximately 5; high phosphatase activity) and eutrophic Rímov reservoir (pH approximately 7-10; moderate phosphatase activity) were incubated with ELFP for 5-300 min, fixed with HgCl2 and filtered through polycarbonate filters. Relative fluorescence of filter-retained ELFA precipitates was quantified with image analysis. Time-courses of ELFA formation exhibited lag periods followed by finite periods of linear increase. In Plesné Lake, lag-times were shorter (1-18 min) and rates of increase in ELFA fluorescence higher (by approximately 2 orders of magnitude) than in Rímov reservoir (lag-times 30-200 min). Similar patterns of ELFA formation kinetics were also observed in Plesné Lake samples in cuvette spectrofluorometer measurements (which failed in Rímov reservoir). Linear regression of seasonal data on rates of increase in ELFA fluorescence from image cytometry and spectrofluorometry (r2 = 0.65, n = 10) allowed for calibration of image cytometry in terms of amount of cell-associated ELFA. Preliminary measurements of extracellular phosphatase activities of several algae resulted in rates (10-2260 fmol cell-1 h-1) which are comparable to data reported in the literature for algal cultures.

Czech Republic↗
PubMed2002

Tree balance, time slices, and evolutionary turnover in cretaceous planktonic foraminifera.

Studies of phylogenetic tree shape often concentrate on the balance of phylogenies of extant taxa. Paleontological phylogenies (which include extinct taxa) can contain additional useful information and can directly document changes in tree shape through evolutionary time. Unfortunately, the inclusion of extinct taxa lowers the power of direct examinations of tree balance because it increases the range of tree shapes expected under null models of evolution (with equal rates of speciation and extinction across lineages). A promising approach for the analysis of tree shape in paleontological phylogenies is to break the phylogeny down into time slices, examining the shape of the phylogeny of taxa alive at each time slice and changes in that shape between successive time slices. This method was illustrated with 57 time slices through a stratophenetic phylogeny of the Cretaceous planktonic foraminiferal superfamily Globotruncanacea. At 3 of 56 intervals between time slices, 93-92.5 million years ago (MYA), 89-88.5 MYA, and 85.5-84 MYA, the group showed steep increases in imbalance. Although none of these increases were significant after Bonferroni correction, these points in the history of the Globotruncanacea were nevertheless identified as deserving of further macroevolutionary investigation. The 84 MYA time slice coincides with a peak in species turnover for the superfamily. Time slices through phylogenies may prove useful for identifying periods of time when evolution was proceeding in a nonstochastic manner.

Biological Evolution↗
PubMed2001

Effects of photocatalytic reactions on marine plankton: titanium dioxide powder as catalyst on the body surface.

Photocatalytic effects of TiO2 powder on marine plankton were examined by the use of either brine shrimp Artemia salina or noxious red tide flagellate Chattonella antiqua as a probe. After UV (365 nm) irradiation for ca. 1 hour, A. salina stopped moving and the body surface was completely covered by TiO2 powder. Similar photoirradiation of C. antiqua, on the other hand, induced deformation of the body from spindle to round shape within 20 minutes. The deformed C. antiqua recovered to normal shapes, when the cells were kept in the same conditions but without UV irradiation for more than 40 minutes. On the prolonged UV irradiation (more than 100 minutes), however, the cells burst and came to annihilation. The photocatalytic reactions of TiO2 on the body surface are thus concluded to induce fatal damages to these microorganisms.

Animals↗
PubMed2004

On a cell-growth model for plankton.

The frequency distribution of diatoms (microscopic unicellular alga with silicified cell-walls, found as plankton) is shown to evolve in time as a steady-size distribution with constant shape, scaled by time. This distribution is preserved when the division occurs at a fixed size into two daughter cells of half-size. In cases where the parameters for growth, division frequency, dispersion and mortality are constants, the frequency distributions can be found explicitly and thus provide a benchmark for computations in more complex cases.

Cell Division↗
PubMed2004

Efficacy of antiseptics and disinfectants on clinical and environmental yeast isolates in planktonic and biofilm conditions.

The aim of this study was to evaluate the efficacy of five antiseptics, three surface disinfectants and UV radiation against a wide range of clinical and environmental yeast isolates. Their efficacy against pure cultures, yeast mixtures and biofilms (prepared by culturing yeasts in Sabouraud broth containing a final concentration of 8% glucose) was tested. Three clinical isolates of Candida albicans, Cryptococcus neoformans and Rhodotorula rubra, and two environmental isolates of Candida albicans and Cryptococcus uniguttulatus were selected. For seven out of eight biocides tested (Betadine, Dermacide, Chlorhexidine, Dosisepsine, hydrogen peroxide, sodium hypochlorite, 70% alcohol, 0.5% Ecodiol) and for UV radiation, susceptibility did not differ according to genus, species or origin. Hydrogen peroxide, 0.25% Ecodiol and UV radiation were ineffective against the five isolates tested. On pure planktonic cultures, and, to a lesser extent, on free-living yeast mixtures, the other products were active and were then tested against biofilms: eight out of nine biocides were ineffective. Chlorhexidine at 0.5% was the only fungicidal agent on pure cultures, yeast mixtures and biofilms. The importance of the test method, including agent concentration, is discussed.

Anti-Infective Agents, Local↗
PubMed2002

Effects of climate warming, North Atlantic Oscillation, and El Niño-Southern Oscillation on thermal conditions and plankton dynamics in northern hemispheric lakes.

Impacts of climate warming on freshwater ecosystems have been documented recently for a variety of sites around the globe. Here we provide a review of studies that report long-term (multidecadal) effects of warming trends on thermal properties and plankton dynamics in northern hemispheric lakes. We show that higher lake temperatures, shorter periods with ice cover, and shorter stagnation periods were common trends for lakes across the hemisphere in response to the warmer conditions. Only for shallow dimictic lakes was it observed that deep-water temperatures decreased. Moreover, it became evident that phytoplankton dynamics and primary productivity altered in conjunction with changes in lake physics. Algal spring blooms developed early and were more pronounced in several European lakes after mild winters with short ice cover periods, and primary productivity increased in North American lakes. Effects of elevated temperatures on zooplankton communities were seen in an early development of various species and groups, as is documented for cladocerans, copepods, and rotifers in European lakes. Furthermore, thermophile species reached higher abundance in warmer years. Obviously, the nature of responses is species specific, and depends on the detailed seasonal patterning of warming. Complex responses such as effects propagating across trophic levels are likely, indicating that observed climate-ecosystem relationships are not generally applicable. Nonetheless, the picture emerges that climate-driven changes in freshwater ecosystems may be synchronised to a certain extent among lakes even over great distances if climatic influences are not masked by anthropogenic impacts or differences in lake morphology. Macro-scale climatic fluctuations--such as the North Atlantic Oscillation or the El Niño-Southern Oscillation--were identified as the most important candidates responsible for such coherence, with the former predominating in Europe and the latter in North America. We emphasise, however, that the driving mechanisms and the future behaviour of these oscillations are rather uncertain, which complicates extrapolation of observed effects into the future. Thus, it is necessary to quantify the most important climate-ecosystem relationships in models of appropriate complexity. Such models will help elucidate the multiple pathways climate affects freshwater ecosystems, and will indicate possible adverse effects of a warmer future climate.

Animals↗