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At least 217 records · Page 12Linked to original sources
PubMed1986

Carbon and nitrogen content of natural planktonic bacteria.

A method of estimating carbon and nitrogen content per unit of natural bacterial cell volume was developed. This method is based on the difference in the retentiveness of bacteria between two kinds of glass fiber filter, GF/C and GF/F (Whatman, Inc., Clifton, N.J.). Biovolume and biomass (carbon and nitrogen content) of bacteria which passed through the GF/C but not the GF/F filter were estimated with an epifluorescence microscopy and a CHN analyzer, respectively. From seasonal determinations of natural planktonic bacteria in epilimnetic waters of a mesotrophic lake, the conversion factors of 106 fg of C/mum and 25 fg of N/mum were derived as average values. By using these values, the contribution of bacteria to the biomass of lake plankton is discussed.

Journal Article↗
PubMed1986

Production and turnover of planktonic bacteria in two southeastern blackwater rivers.

Production by attached and free-living planktonic bacteria in two blackwater rivers in the Southeastern United States was measured over a period of 14 months by using the rate of incorporation of [methyl-H]thymidine into DNA. Production rates and biomass dynamics were compared to determine the potential for in situ production to supply planktonic biomass. Bacterial production in these rivers was moderate and varied seasonally. Rates varied from 0.058 to 2.120 mg of C m h in the Ogeechee River and from 0.002 to 2.418 mg of C m h in Black Creek. Regressions of growth rate on various environmental variables showed that temperature and total dissolved organic carbon concentration were the best predictors of growth. Although attached bacteria were <21% of the total biomass, they accounted for up to 53% of the total production. Turnover times for attached bacteria ranged from <1 day to >3 years depending on season. Turnover times of free-living bacteria varied from 4.4 days to 11.8 years. Comparisons of biomass with production indicated that during most seasons, the majority of bacterial biomass in these rivers was of allochthonous origin. During summer, when water temperatures were high, bacterial growth in the river may have supplied a greater percentage of the standing stock of bacteria than allochthonous inputs.

Journal Article↗
PubMed1988

Extraction from natural planktonic microorganisms of DNA suitable for molecular biological studies.

We developed a simple technique for the high-yield extraction of purified DNA from mixed populations of natural planktonic marine microbes (primarily bacteria). This is a necessary step for several molecular biological approaches to the study of microbial communities in nature. The microorganisms from near-shore marine and brackish water samples, ranging in volume from 8 to 40 liters, were collected on 0.22-mum-pore-size fluorocarbon-based filters, after prefiltration through glass fiber filters, to remove most of the eucaryotes. DNA was extracted directly from the filters in 1% sodium dodecyl sulfate that was heated to 95 to 100 degrees C for 1.5 to 2 min. This procedure lysed essentially all the bacteria and did not significantly denature the DNA. The DNA was purified by phenol extraction, and precautions were taken to minimize shearing. Agarose gel electrophoresis showed that most of the final preparation had a large molecular size (>23 kilobase pairs). The DNA was sufficiently pure to allow complete digestion by the restriction endonuclease Sau3AI and ligation to vector DNA. In a sample in which the extracted DNA was quantified by binding to the dye Hoechst H33258, DNA was quantitatively extracted, and 45% of the initially extracted DNA was recovered after purification. Final yields were a few micrograms of DNA per liter of seawater and were roughly 25 to 50% of the total bacterial DNA in the sample. Alternatives to the initial harvest by filtration method, including continuous-flow centrifugation and thin-channel or hollow-fiber concentration followed by centrifugation, were less efficient than filtration in terms of both time and yield, largely because of the difficulty of centrifuging the very small bacteria typical of marine plankton. These methods were judged to be less appropriate for studies of natural populations as they impose a strong selection for the larger bacteria.

Journal Article↗
PubMed1990

Rapid quantification of planktonic ciliates: comparison of improved live counting with other methods.

THE FOLLOWING EFFICIENT AND QUANTITATIVELY VALID METHOD TO FILTER CONCENTRATE AND COUNT LIVE PLANKTONIC CILIATES WAS DEVELOPED AND COMPARED WITH OTHER TREATMENTS: unconcentrated (raw) samples and centrifuged samples were counted live, and the effects of five different fixatives (HgCl(2), Lugol's iodine, formaldehyde, glutaraldehyde, and Champy-DaFano) on the counts were monitored. Samples originated from a eutrophic mountain lake (Lake Aydat, near Clermont-Ferrand, France). Overall, live filtered counts were similar to counts of raw samples, but they were significantly higher (2 to 2.3 fold, P < 0.05) by analysis of variance than counts from centrifuged samples. Nevertheless, some taxa, i.e., Halteria and Loxodes spp., were sensitive to filtration. The live filtered counts were also comparable to counts of raw HgCl(2)-fixed and settled samples. HgCl(2) and Lugol fixation consistently gave the highest total counts, while significantly lower counts were always obtained with Champy-DaFano-fixed samples. Losses due to fixation were insignificant for raw samples but were substantial and statistically significant in concentrated samples (15% after filtration and 71% after centrifugation, compared with counts from the corresponding live samples). Live counting of passively filter-concentrated ciliates has many advantages over other methods. It is two to four times quicker and more efficient. Ciliates are recognized with certainty, more species are identified, and enumeration of dead organisms (e.g., tintinnid loricas) is avoided. It should be recommended as a quantitatively valid alternative to classical methods for assessing planktonic ciliate populations.

Journal Article↗
PubMed1997

Ether lipids of planktonic archaea in the marine water column.

Acyclic and cyclic biphytanes derived from the membrane ether lipids of archaea were found in water column particulate and sedimentary organic matter from several oxic and anoxic marine environments. Compound-specific isotope analyses of the carbon skeletons suggest that planktonic archaea utilize an isotopically heavy carbon source such as algal carbohydrates and proteins or dissolved bicarbonate. Due to their high preservation potential, these lipids provide a fossil record of planktonic archaea and suggest that they have thrived in marine environments for more than 50 million years.

Journal Article↗
PubMed2004

Adhesion of Enterococcus faecalis in the nonculturable state to plankton is the main mechanism responsible for persistence of this bacterium in both lake and seawater.

The presence of enterococci in lake and seawater in an 18-month survey comparing molecular (PCR and quantitative PCR) and culture methods was evaluated, as well as the possibility that zooplankton could act as reservoirs for enterococci. Samples of both water and zooplankton were collected monthly from a Lake Garda site and an Adriatic Sea site. In lake water, the positive samples numbered 13 of 54 (24%) by culture and 32 of 54 (59%) when PCR was applied. In seawater, they numbered 0 of 51 by culture and 18 of 51 (35%) by PCR. Enterococci were found either totally bound to plankton or totally in water, depending on the presence or absence of plankton, respectively. These results clearly indicate that the PCR assay is a powerful tool for detecting fecal indicators and pathogens in the environment, thus providing a much more sensitive method than culture.

Animals↗
PubMed1998

Photoreception in the planktonic larvae of two species of pullosquilla, a lysiosquilloid stomatopod crustacean

Optical microscopy, electron microscopy and microspectrophotometry were used to characterize pigments in the eyes of planktonic larvae of two species of the lysiosquilloid stomatopod Pullosquilla, P. litoralis and P. thomassini, which live sympatrically in French Polynesia. In contrast to the adult retina, which contains a diverse assortment of visual pigments in the main rhabdoms, the principal photoreceptors throughout the larval eyes of both species were found to contain a single rhodopsin with an absorption maximum ( max) close to 446 nm. The expression of this visual pigment may survive metamorphosis, since several adult rhodopsins occur at a similar spectral position. The retinas of these planktonic larvae also contain a novel yellow photostable pigment, which is arrayed in a regular pattern at the distal margin of the larval retina. The absorption spectrum of this pigment is well matched to the larval rhodopsin, suggesting that it acts to screen the rhabdoms from stray light. By replacing opaque, black screening pigment, the transparent yellow pigment may act together with a blue iridescent layer in the larval retina to reduce the visual contrast of the larval eye against downwelling and sidewelling light, while simultaneously acting as a retinal screen.

Journal Article↗
PubMed1999

Chloramine and copper sulfate as control agents of planktonic larvae of Chironomus luridus in water supply systems.

The latest approach to control of midge larvae in drinking-water supplies is suppression of the planktonic 1st-stage larvae, by using 2 disinfectants, chloramine and copper sulfate. The median lethal concentration for 24-h exposure of the 1st-stage larvae of Chironomus luridus to chloramine and copper sulfate individually was 0.51 and 0.38 mg/liter, respectively. The increase of copper sulfate to 0.5 mg of copper per liter to water containing chloramine (0.5 mg/liter) created a synergistic reaction that resulted in 96% (+/-8% SD) mortality of the planktonic larvae. This treatment may serve as an effective control of 1st-stage larvae in municipal drinking-water supplies.

Animals↗
PubMed2002

How does time-dependent dental unit waterline flushing affect planktonic bacteria levels?

The purpose of this study was to evaluate how time-dependent waterline flushing affects the presence of biofilm in otherwise-untreated dental unit waterlines (DUWLs). Water samples were obtained from twelve highspeed handpiece DUWLs located in the undergraduate treatment clinic at the University of Missouri-Kansas City, School of Dentistry. Baseline water samples (50 cc) were collected prior to the start of continuous flushing. Additional 50 cc samples were collected after two-, three-, and four-minute flushing intervals from the baseline. The levels of planktonic bacteria in DUWLs were quantified by counting colony forming units (CFUs). In addition, segments of water tubing from each of the highspeed handpiece waterlines were examined by scanning electron microscopy, which confirmed the presence of a residual biofilm in the lumen of each dental unit waterline. A one-factor repeated measures ANOVA showed a statistically significant (p<0.01) reduction in CFUs at all intervals compared to baseline and between each successive time interval. Indeed, after four minutes of continuous flushing, all waterlines still harbored CFU levels that exceed current American Dental Association (ADA) recommendations. It was concluded that water flushing of DUWLs produced a statistically significant reduction in planktonic bacteria at each time interval compared to the baseline and between each successive time interval. However, the level of CFUs after four minutes of continuous water flushing still exceeds the current ADA recommendations for acceptable levels of microorganisms.

Analysis of Variance↗
PubMedDate not supplied

[Mechanisms responsible for the development of periphyton community structure during seasonal succession: the role of interspecies competition and plankton sedimentation].

The development of periphyton community structure by exchange of organisms between substratum and water column (noninteractive mechanism) and by interspecific competition for surface (interactive mechanism) was studied during seasonal succession in Akulovsky water supply channel (the Upper Volga basin). The influence of exchange was assumed by similarity between the species composition of plankton and periphyton. At early stages of succession when the diatoms dominated in periphyton the community was formed mainly by phytoplankton sedimentation, while the competition for substratum didn't result in decrease of species diversity because the poor competitors were partly displaced by new colonists from the water column. Later when the green filamentous algae abundantly developed in periphyton, their numbers were probably controlled by factors not related to exchange of propagules. At the same time, the species structure of secondary periphyton cover developing on the thallus of filamentous algae depended mainly on the plankton sedimentation. At the last stages of seasonal succession when periphyton was represented by colonies of cyanobacteria and diatoms closely covering the substratum, the exchange of organisms between substratum and water column was not so important as interspecific competition for surface. As one could suppose, increase in biomass in this period resulted in the decrease of specificity as it was predicted by hypothesis of interactive community. In such a way, both mechanisms (interactive and noninteractive ones) took part in development of periphyton structure. Their relative influence changed in the course of seasonal succession.

Biomass↗
PubMed2005

[Comparison of ALS gene mRNA between sessile and planktonic Candida albicans of oral cavities].

OBJECTIVE: To observe the different mRNA levels of Candida albicans ALS gene family between planktonic and biofilm-grown cells. METHODS: ATCC 90038 and a wild strain of Candida albicans, biofilm models in vitro were formed on glass slides. After 48 hours' incubation, the biofilm-grown cells were harvested. Half-quantification of ALS1 and ALS4 mRNA was based on the amplification by one-step RT-PCR. RESULTS: The amounts of ALS1 and ALS4 mRNA of the wild strain in biofilm increased comparing with planktonic cells, while ATCC 90038 didn't. CONCLUSION: The members of ALS gene family may play important roles in the course of Candida albicans biofilm formation.

Biofilms↗
PubMed1994

The Macro Flow Planktometer: a new device for volume and fluorescence analysis of macro plankton including triggered video imaging in flow.

A newly developed macro flow planktometer is described for measuring plankton organisms with a size of 100-2,000 microns by the flow principle in time-saving and noncontact fashion. Based on the method of changes in electric resistance (Coulter principle), the device allows determination of the body volume of living organisms in their natural medium (fresh or seawater) at a measuring rate of up to 50 organisms per second. Simultaneous, laser-excited fluorescence measurement permits quantitative detection of fluorescent substances within the organisms. Controlled by the multiparametric measurement, video images of organisms of particular interest can be taken in the flow chamber using a stroboscopic imaging system. Valuable morphological information on the material under test is thus available in addition to the analytical measurement. Data acquisition and imaging, the total system control, and the fast data evaluation are performed with an IBM-AT compatible computer using an extensive software package. The easy-to-handle desktop unit can be used both in land laboratories and on ships. The modular structure of the system permits any desired combination of individual components to adapt it to various requirements. The operability of this new measuring system is demonstrated by several applications.

Animals↗
PubMed2006

Comparative proteome analysis of Staphylococcus aureus biofilm and planktonic cells and correlation with transcriptome profiling.

Pathogenic staphylococci can form biofilms in which they show a higher resistance to antibiotics and the immune defense system than their planktonic counterparts, which suggests that the cells in a biofilm have an altered metabolic activity. Here, 2-D PAGE was used to identify secreted, cell wall-associated and cytoplasmic proteins expressed in Staphylococcus aureus after 8 and 48 h of growth. The proteins were separated at pH ranges of 4-7 or 6-11. The protein patterns revealed significant differences in 427 protein spots; from these, 258 non-redundant proteins were identified using ESI-MS/MS. Biofilm cells expressed higher levels of proteins associated with cell attachment and peptidoglycan synthesis, and in particular fibrinogen-binding proteins. Enzymes involved in pyruvate and formate metabolism were upregulated. Furthermore, biofilm cells expressed more staphylococcal accessory regulator A protein (SarA), which corroborates the positive effect of SarA on the expression of the intercellular adhesion operon ica and biofilm growth. In contrast, proteins, such as proteases and particularly immunodominant antigen A (IsaA) and staphylococcal secretory antigen (SsaA), were found in lower amounts. The RNA expression profiling largely supports the proteomic data. The results were mapped onto KEGG pathways.

Bacterial Proteins↗
PubMed2000

Planktonic contact rates in homogeneous isotropic turbulence: theoretical predictions and kinematic simulations.

The key role played by turbulence in the environment of plankton and larval fish populations has become appreciated in recent years. In particular, the turbulent enhancement of encounter rates between different species of microorganisms, either swimming or passively advected by the flow, is well established. However, most of the current modelling approaches are rather ad hoc, giving rise to ambiguities in the specification of certain key parameters. In this paper, the encounter problem in a turbulent flow of large Reynolds number is re-examined from first principles and a number of new formulae will be established for different swimming strategies. The key innovation is the proposal of a model form for the conditional joint probability density function of predator and prey velocities when the organisms are separated by their given contact radius, R. Particular attention will be paid to the case when a microorganism follows a random trajectory, due to a combination of its own swimming and the action of the flow. The theoretical predictions are subsequently tested against corresponding quantities derived from a series of kinematic simulations of a turbulent-like flow field. Good agreement is demonstrated between the predictions and simulations.

Animals↗
PubMed2001

Oscillations in plankton models with nutrient recycling.

Plankton--nutrient interaction models with both instantaneous and delayed nutrient recycling are considered. The system consists of three components: autotrophic phytoplankton, herbivorous zooplankton and dissolved limiting nutrient. Local stability of the equilibria is analysed. It is shown that the positive equilibrium loses its stability when the nutrient input concentration passes through a critical value and the Hopf bifurcation occurs that induces oscillations of the populations. Numerical simulations are carried out to illustrate the obtained results.

Animals↗
PubMed2001

The influence of turbulence on plankton predation strategies.

The importance of predation in regulating the size of competing plankton and larval fish populations has long been appreciated. However, it has only recently been recognized that turbulence must have a significant influence on predator-prey interactions because most rival species of microorganisms co-exist in oceanic or fast moving fresh water flows. Turbulence is likely to influence predation strategies in two ways. The extra energy imparted to a micro-organism from the flow field will enhance the number of encounters or "contacts" between predators and prey. At the same time, because the velocity of a predator relative to its potential prey will be increased, the time-scale over which a capture must be completed is reduced. Balancing the benefits of extra encounters with the drawbacks of more difficult captures, will dictate an optimal predation strategy, either foraging behaviour or ambush feeding, on the predator. This will depend on its own and the prey's swimming capabilities, as well as the characteristics of the turbulent environment. In this paper some previous work, examining the increased encounter rate in turbulence, will be extended to look at the capture problem. The main proposal is that the capture event should be encapsulated in a capture probability function, from which the optimal predation strategy can be derived. As an illustration, plausible capture probability functions will be postulated and the resulting predictions tested against numerical simulations carried out in a turbulent-like flow field. Good agreement between the predictions and the simulations is demonstrated.

Animal Nutritional Physiological Phenomena↗
PubMed2002

Stoichiometry, herbivory and competition for nutrients: simple models based on planktonic ecosystems.

Models are examined in which two prey species compete for two nutrient resources, and are preyed upon by a predator that recycles both nutrients. Two factors determine the effective relative supply of the nutrients, hence competitive outcomes: the external nutrient supply ratio, and the relative recycling of the two nutrients within the system. This second factor is governed by predator stoichiometry--its relative requirements for nutrients in its own biomass. A model with nutrient resources that are essential for the competing prey is detailed. Criteria are given to identify the limiting nutrient for a food chain of one competitor with the predator. Increased supply of this limiting nutrient increases predator density and concentration of this nutrient at equilibrium, while decreasing the concentration of a non-limiting nutrient. Changes in supply or recycling of a non-limiting nutrient affect only the concentration of that nutrient. Criteria for the invasion of a second prey competitor are presented. When different nutrients limit growth of the resident prey and the invader, increased supply or recycling of the invader's limiting nutrient assists invasion, while increased supply or recycling of the resident's limiting nutrient hinders invasion. If the same nutrient limits both resident and invader, then changes in supply and recycling have complex effects on invasion, depending on species properties. In a parameterized model of a planktonic ecosystem, green algae and cyanobacteria coexist over a wide range of nitrogen:phosphorus supply ratios, without predators. When the herbivore Daphnia is added, coexistence is eliminated or greatly restricted, and green algae dominate over a wide range of supply conditions, because the effective supply of P is greatly reduced as Daphnia rapidly recycles N.

Animals↗
PubMed1998

Molecular versus taxonomic rates of evolution in planktonic foraminifera.

Neogene planktonic foraminifera are among the most widely used microfossils in the study of tempo and mode of evolution. Comparisons of taxonomic rates between the two major clades in this group have shown that the nonspinose globorotaliids have undergone a significantly more rapid evolutionary turnover than the spinose globigerinids (S. M. Stanley et al., 1988, Paleobiology 14, 235-249). In order to test if similar fluctuations are observed in molecular data, we have used different methods to calculate absolute and relative rates of substitutions based on 16 partial SSU rDNA sequences from representatives of both groups. According to our data, rates of substitution are relatively constant within the globigerinids with a mean value of 4.3 subst./site/10(9) years, but vary in the globorotaliid clade with three species having a rate of about 1 subst./site/10(9) years and two species evolving much faster with rates of more than 7 subst./site/10(9) years. Assuming that the fast rates result from recent accelerations, the globorotaliids have basically much slower molecular evolutionary rates than the globigerinids, in opposition to the fossil data.

Animals↗