1992

mardi 21 avril 2009
par   G. Grégori

Andreoli C, Scarabel L, Spini S, Grassi C (1992) The Picoplankton in Antarctic Lakes of Northern Victoria-Land during Summer 1989-1990. Polar Biology 11 :575-582

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Photoautotrophic picoplankton is reported from some lakes located near the Italian Antarctic station of Terra Nova. Observations, carried out by both flow cytometry on water samples and electron microscopy on micro-organisms in cultures from each lake, have confirmed the occurrence in all the environments studied of this fraction accounting, in several cases, for more than the 50% of the phytoplankton, measured as chlorophyll. Cultures of the picoplankton fraction from these waters contained known prokaryotic (Synechococcus) and eukaryotic (Chlorella) genera as well as two unidentified entities, possibly prochlorophytes.


Blanchot J, Rodier M, Lebouteiller A (1992) Effect of El-Nino Southern Oscillation Events on the Distribution and Abundance of Phytoplankton in the Western Pacific Tropical Ocean Along 165-Degrees-E. Journal of Plankton Research 14 :137-156

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The distribution of physical and chemical parameters and their impact on the biomass and abundance of phytoplankton in the Western Pacific Ocean were compared in two opposing situations : the El Nino Southern Oscillation (ENSO) event of 1987 and the non-ENSO period of 1988. During El Nino conditions (September 1987), maximum cell abundance was recorded at 10-degrees-S at the boundary between the South Equatorial Current (SEC) and the South Equatorial Countercurrent (SECC). In September 1988, after the return of non-ENSO conditions, a well-established equatorial upwelling produced an increase in the sur-face layer nutrient supply over 7-degrees of latitude. This in turn caused an increase in phytoplankton populations in the upper layer, with chlorophyll concentrations > 0.2 mg m-3 and cyanobacteria and microalgae populations > 8.0 x 10(6) l-1 and > 1.2 x 10(6) l-1 respectively. Integrated over 120 m, the cyanobacteria and microalgae populations were respectively 4.7 and 3.2 times larger than the year before. On the other hand, transient nutrient inputs such as those observed at 10-degrees-S in September 1987 caused a large increase in cyanobacteria populations (4.4 times), compared with those in neighboring zones, and a somewhat smaller increase in microalgae populations (1.3 times). Cyanobacteria populations were much larger than those of microalgae in the 80-100 m upper layer, whereas the latter were more numerous at that depth and below the chlorophyll maximum. Population variations in cyanobacteria were accompanied by changes in form, size and fluorescence of the cells. The analysis of the 52 profiles of depth distribution of cyanobacteria and microalgae shows how the community structure is related to the depth and gradient of the nitracline.


Broenkow WW, Yuen MA, Yarbrough MA (1992) Vertex - Biological Implications of Total Attenuation and Chlorophyll and Phycoerythrin Fluorescence Distributions Along a 2000-M Deep Section in the Gulf of Alaska. Deep-Sea Research Part a-Oceanographic Research Papers 39 :417-437

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A 2000 m deep section of total attenuation and chlorophyll and phycoerythrin fluorescence from 26-degrees to 59-degrees-N latitude in the northeast Pacific is discussed in terms of inferred biological processes. Photic zone distributions of these quantities vary from nutrient-limited conditions in the subtropics to light-limited conditions in the subarctic. Phycoerythrin-containing organisms, probably Synechococcus, contribute to a strong, near-surface orange fluorescence signal in the Gulf of Alaska. We now recognize that the fluorescence minimum (about 300 m) between the photic zone and the tertiary fluorescence maximum may be related to secondary producers that "repackage" organic matter produced in the photic zone. The tertiary fluorescence maximum (about 1000 m) is a continuous feature of the oxygen minimum zone in the North Pacific. The presence of phycoerythrin in the tertiary maximum is consistent with heterotrophic cyanobacteria and other unidentified microbial assemblages in the oxygen minimum, though there is no strong biological evidence that this is true.


Button DK, Robertson BR, McIntosh D, Juttner F (1992) Interactions between marine bacteria and dissolved-phase and beached hydrocarbons after the Exxon Valdez oil spill. Appl Environ Microbiol 58 :243-251

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Turnover times for toluene in Resurrection Bay after the Exxon Valdez grounding were determined to be decades, longer than expected considering that dissolved hydrocarbons were anticipated to drift with the current and stimulate development of additional hydrocarbon-utilizing capacity among the microflora in that downcurrent location. These turnover times were based on the recovery of 14CO2 from added [14C]toluene that was oxidized. The concentrations of toluene there, 0.1 to 0.2 microgram/liter, were similar to prespill values. Oxidation rates appeared to be enhanced upstream near islands in the wake of the wind-blown slick, and even more within the slick itself. Specific affinities of the water column bacteria for toluene were computed with the help of biomass data, as measured by high-resolution flow cytometry. They were a very low 0.3 to 3 liters/g of cells.h-1, indicating limited capacity to utilize this hydrocarbon. Since current-driven mixing rates exceeded those of oxidation, dissolved spill components such as toluene should enter the world-ocean pool of hydrocarbons rather than biooxidize in place. Some of the floating oil slick washed ashore and permeated a coarse gravel beach. A bacterial biomass of 2 to 14 mg/kg appeared in apparent response to the new carbon and energy source. This biomass was computed from that of the organisms and associated naphthalene oxidation activity washed from the gravel compared with the original suspension. These sediment organisms were very small at approximately 0.06 microns 3 in volume, low in DNA at approximately 5.5 g per cell, and unlike the aquatic bacteria obtained by enrichment culture but quite similar to the oligobacteria in the water column.(ABSTRACT TRUNCATED AT 250 WORDS)


Button DK, Robertson BR, Mcintosh D, Juttner F (1992) Interactions between Marine-Bacteria and Dissolved-Phase and Beached Hydrocarbons after the Exxon-Valdez Oil-Spill. Applied and Environmental Microbiology 58 :243-251

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Turnover times for toluene in Resurrection Bay after the Exxon Valdez grounding were determined to be decades, longer than expected considering that dissolved hydrocarbons were anticipated to drift with the current and stimulate development of additional hydrocarbon-utilizing capacity among the microflora in that downcurrent location. These turnover times were based on the recovery of (CO2)-C-14 from added [C-14]toluene that was oxidized. The concentrations of toluene there, 0.1 to 0.2-mu-g/liter, were similar to prespill values. Oxidation rates appeared to be enhanced upstream near islands in the wake of the wind-blown slick, and even more within the slick itself. Specific affinities of the water column bacteria for toluene were computed with the help of biomass data, as measured by high-resolution flow cytometry. They were a very low 0.3 to 3 liters/g of cells . h-1, indicating limited capacity to utilize this hydrocarbon. Since current-driven mixing rates exceeded those of oxidation, dissolved spill components such as toluene should enter the world-ocean pool of hydrocarbons rather than biooxidize in place. Some of the floating oil slick washed ashore and permeated a coarse gravel beach. A bacterial biomass of 2 to 14 mg/kg appeared in apparent response to the new carbon and energy source. This biomass was computed from that of the organisms and associated naphthalene oxidation activity washed from the gravel compared with the original suspension. These sediment organisms were very small at almost-equal-to 0.06-mu-m3 in volume, low in DNA at almost-equal-to 5.5 g per cell, and unlike the aquatic bacteria obtained by enrichment culture but quite similar to the oligobacteria in the water column. Activity toward hydrocarbons was moderate, with specific affinities for naphthalene of 26 to 92 liters/g of cells/b (V(max), 0.36-mu-g/g of cells . h-1 ; K(m), 1.4-mu-g/liter), giving residence times of only a few hours. A large population of carbon- and energy-starved, induced hydrocarbon oxidizers with metabolism limited by the physical and molecular recalcitrance of the heavier components is suggested. These are factors that should be addressed in bioremediation efforts. The effects of a surfactant that was widely applied were unremarkable on a test beach after 1.5 months. Unresolved components appearing in chromatograms from the remaining mixture were characteristic of partial oxidation products. Such compounds, known to accumulate when concentrations of smaller aqueous-phase hydrocarbons exceed the K(m), may form in sediments as well.


Chisholm SW, Frankel SL, Goericke R, Olson RJ, Palenik B, Waterbury JB, Westjohnsrud L, Zettler ER (1992) Prochlorococcus-Marinus Nov Gen-Nov Sp - an Oxyphototrophic Marine Prokaryote Containing Divinyl Chlorophyll-a and Chlorophyll-B. Archives of Microbiology 157 :297-300

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Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world’s tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins. and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte ’relatives’ Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus.


Demers S, Kim J, Legendre P, Legendre L (1992) Analyzing multivariate flow cytometric data in aquatic sciences. Cytometry 13 :291-298

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Flow cytometry has recently been introduced in aquatic ecology. Its unique feature is to measure several optical characteristics simultaneously on a large number of cells. Until now, these data have generally been analyzed in simple ways, e.g., frequency histograms and bivariate scatter diagrams, so that the multivariate potential of the data has not been fully exploited. This paper presents a way of answering ecologically meaningful questions, using the multivariate characteristics of the data. In order to do so, the multivariate data are reduced to a small number of classes by clustering, which reduces the data to a categorical variable. Multivariate pairwise comparisons can then be performed among samples using these new data vectors. The test case presented in the paper forms a time series of observations from which the new method enables us to study on the temporal evolution of cell types.


Furuya K, Li WKW (1992) Evaluation of Photosynthetic Capacity in Phytoplankton by Flow Cytometric Analysis of Dcmu-Enhanced Chlorophyll Fluorescence. Marine Ecology-Progress Series 88 :279-287

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A new method is presented to evaluate the photosynthetic capacity of individual phytoplankton cells using flow cytometry. The method is based on the well-known phenomenon in which chlorophyll a fluorescence is enhanced in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport. Using a mercury-cadmium arc lamp-based flow cytometer, we found significant correlations between fluorescence enhancement and photosynthetic capacity. The correlation was dependent on species and growth irradiance. The regression coefficient ranged more than 5 times according to species, and cells under light-saturated growth were enhanced less than light-limited cells, although the former had higher photosynthetic capacity than the latter. The ability to measure DCMU-enhanced fluorescence in flow cytometry depends on a weak excitation beam and a long residence time in the sensing zone to ensure maximum variable fluorescence yield. We were unable to detect enhancement using laser-based flow cytometers. The variability in fluorescence enhancement is discussed in relation to its practical use in the field. The method was applied to natural assemblages in Bedford Basin (Canada) : temporal variations of fluorescence enhancement were clearly evident in dominant diatoms and cryptophytes.


Hofstraat JW, Rubelowsky K, Slutter S (1992) Corrected Fluorescence Excitation and Emission-Spectra of Phytoplankton - toward a More Uniform Approach to Fluorescence Measurements. Journal of Plankton Research 14 :625-636

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Techniques for correction of fluorescence emission and excitation spectral of phytoplankton are described. which can be applied in any commercially available spectrophotometer. The correction of the emission spectrum is based on the measurement of a calibrated light source. The excitation spectra are corrected by means of a quantum counter solution that measures the spectral intensity of the excitation system and separate correction for wavelength-dependent effects of the excitation optics. The correction procedures give technically corrected spectra, i.e. spectral that are free from wavelength dependent bias, but do not give absolute intensity values. Spectra that have been properly corrected for instrumental wavelength dependencies are suitable for intercomparison, both intra- and interlaboratory. Another application is the derivation of spectral data that will be obtained by other techniques that make use of fluorescence measurements, Such as flow cytometry, remote sensing and in situ instruments. A necessary condition is that the spectral response functions of these instruments must be known.


Kaprelyants AS, Kell DB (1992) Rapid Assessment of Bacterial Viability and Vitality by Rhodamine 123 and Flow-Cytometry. Journal of Applied Bacteriology 72 :410-422

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The fluorescent dye rhodamine 123 (Rh 123) is concentrated by microbial cells in an uncoupler-sensitive fashion. Steady-state fluorescence measurements with Micrococcus luteus indicated that provided the added dye concentration is below approximately 1 mmol/l, uptake is fully uncoupler-sensitive and is not accompanied by significant self-quenching of the fluorescence of accumulated dye molecules. ’Viable’ and ’non-viable’ cells are easily and quantitatively distinguished in a flow cytometer by the extent to which they accumulate the dye. The viability of a very slowly growing chemostat culture of Mic. luteus is apparently only about 40-50%, as judged by plate counts, but most of the ’non-viable’ cells can be resuscitated by incubation of the culture in nutrient medium before plating. The extent to which individual cells accumulate rhodamine 123 can be rapidly assessed by flow cytometry, and reflects the three distinguishable physiological states exhibited by the culture (’non-viable’, ’viable’ and ’non-viable-but-resuscitable’). Gram-negative bacteria do not accumulate rhodamine 123 significantly because their outer membrane is not permeable to it ; a simple treatment overcomes this. Flow cytometry using rhodamine 123 should prove of general utility for the rapid assessment of microbial viability and vitality.


Li WKW, Dickie PM, Irwin BD, Wood AM (1992) Biomass of Bacteria, Cyanobacteria, Prochlorophytes and Photosynthetic Eukaryotes in the Sargasso Sea. Deep-Sea Research Part a-Oceanographic Research Papers 39 :501-519

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Bacteria, cyanobacteria, prochlorophytes and photosynthetic eukaryotes were enumerated in depth profiles at a station in the northern Sargasso Sea occupied for 9 days during September 1988. Carbon biomass of each group was inferred from cell abundance using conversion factors taken from the literature. Over the upper 200 m in the water column, carbon biomass occurred in the approximate proportion of 1:2:4:8 for cyanobacteria : prochtorophytes : photosynthetic eukaryotes:bacteria. Taken together, the three phytoplankton groups represented about the same amount of carbon biomass as the bacteria. This conclusion was validated by the independent measure of bulk chlorophyll a (Chl a) if the carbon:Chl a ratio was assumed to be about 44 in the nitrate-depleted layer and about 15 in the nitrate-rich layer. In reporting the biomass co-dominance of bacteria and phytoplankton, we do not deny that bacteria may dominate phytoplankton at other times and places in the oligotrophic ocean. Biomass co-dominance between these two trophic groups admits the possibility that oligotrophic bacterial assemblages may have high growth rates.


Lyne TB, Bickham JW, Lamb T, Gibbons JW (1992) The Application of Bioassays in Risk Assessment of Environmental-Pollution. Risk Analysis 12 :361-365

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Increased contamination of the environment by toxic chemicals has resulted in the need for sensitive assays to be used in risk assessment of polluted sites. Traditional tests are useful to detect and measure concentrations of chemicals in the environment and in tissues. However, physicochemical assays possess deficiencies that impair their use in evaluating complex environmental contamination. We have developed cytogenetic procedures, including chromosomal, micronucleus, and flow cytometric assays, to assess the mutagenic damage of petrochemicals and low-level radioactivity on indigenous terrestrial and aquatic wildlife populations. These procedures are sensitive to the perturbation of DNA that results from exposure to mutagenic contaminants in both field and laboratory studies. The use of natural populations of animals in biomonitoring, combined with traditional chemical assays, will ultimately provide sufficient information to estimate the risk to human health and environmental quality from anthropogenic pollution.


Monfort P, Baleux B (1992) Comparison of flow cytometry and epifluorescence microscopy for counting bacteria in aquatic ecosystems. Cytometry 13 :188-192

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Flow cytometry was used to count bacterial cells from diverse origins : one strain of E. coli, one sample of lake water, and 18 samples of estuary water. To verify the accuracy and the precision of this technique, total bacteria counts made by flow cytometry were compared with counts by direct observation using epifluorescence microscopy. The results of this study showed that flow cytometry was a reliable technique for counting a mixture of bacteria in samples from aquatic ecosystems.


Monfort P, Baleux B (1992) Comparison of Flow-Cytometry and Epifluorescence Microscopy for Counting Bacteria in Aquatic Ecosystems. Cytometry 13 :188-192

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Flow cytometry was used to count bacterial cells from diverse origins : one strain of E. coli, one sample of lake water, and 18 samples of estuary water. To verify the accuracy and the precision of this technique, total bacteria counts made by flow cytometry were compared with counts by direct observation using epifluorescence microscopy. The results of this study showed that flow cytometry was a reliable technique for counting a mixture of bacteria in samples from aquatic ecosystems.


Orellana MV, Perry MJ (1992) An Immunoprobe to Measure Rubisco Concentrations and Maximal Photosynthetic Rates of Individual Phytoplankton Cells. Limnology and Oceanography 37 :478-490

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The cross-reactivity of an immunological probe to the key photosynthetic enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) was characterized as part of a larger effort to determine maximal photosynthetic rates of individual phytoplankton cells. Polyclonal antiserum was produced against purified Rubisco from the marine diatom Chaetoceros gracilis. The results of western immunoblotting demonstrated that the antiserum reacted positively with Rubisco from 38 species of algae and higher plants and failed to react with only three species of dinoflagellates and one prochlorophyte species. However, the binding affinity or the strength of the cross-reaction for the polyclonal antiserum with purified Rubisco varied among species. The antiserum was then affinity purified against spinach Rubisco and its binding affinity for purified Rubisco determined by ELISA. Two taxonomic groupings resulted : one with high-binding affinity (these species included chrysophytes, bacillariophytes, prymnesiophytes, and chlorophytes) and the other with low-binding affinity (dinophytes and cyanophytes). Rubisco concentration per cell and light-saturated rates of photosynthesis were highly correlated for cultures of the diatom Thalassiosira weissflogii. These results indicate that affinity-purified antiserum can be rigorously characterized for use in quantifying Rubisco concentration and for assessing the maximal photosynthetic potential of individual phytoplankton cells.


Romano TA, Ridgway SH, Quaranta V (1992) MHC class II molecules and immunoglobulins on peripheral blood lymphocytes of the bottlenosed dolphin, Tursiops truncatus. J Exp Zool 263 :96-104

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The immune system of marine mammals is of comparative interest because of its adaptation to the aquatic environment. Little information, however, is available on its cellular and molecular components. Here, we used a cross-reactive antibody to MHC class II molecules and an immunoglobulin-specific antiserum for identifying these molecular species on lymphocytes of the bottlenosed dolphin, Tursiops truncatus. Limited structural analyses indicated that class II molecules and immunoglobulins of dolphin closely resemble those of other vertebrates. In the peripheral blood of most land mammals both class II and immunoglobulins are usually found on B but not T lymphocytes. Expression of immunoglobulins on dolphin peripheral blood lymphocytes suggests a ratio of B cells to T cells comparable to that of land mammals. However, unlike the majority of land mammals, virtually 100% of the peripheral T cells display pronounced expression of class II molecules, generally considered an indication of T cell activation. It is therefore possible that the physiology of T cell activation has unusual attributes in the dolphin. It is especially interesting that some land mammals, namely swine (ungulates) and dogs and cats (carnivores), also express class II molecules on peripheral blood T lymphocytes. Since ungulates and carnivores are thought to share a common distant ancestry with toothed whales, the evolutionary history may be more relevant than the environmental history in determining these unusual attributes.


Savenkoff C, Dasilva NL, Lefevre D, Denis M, Rassoulzadegan F (1992) Contribution of the Different Planktonic Microbial Assemblages to Ets Activity in the Ligurian Frontal Area - North-West Mediterranean-Sea. Journal of Plankton Research 14 :835-850

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Spatial and size distribution of micro-organisms and their ETS activity has been investigated in Ligurian Sea surface waters along the Nice-Calvi transect across frontal areas from 18 to 37 km offshore (TOMOFRONT 1 and 2 cruises, April 1988 and April-May 1989 respectively). Aplastidic and plastidic nanoflagellates and aplastidic picoflagellates were present in numbers close to 0.25 X 10(4) cells ml-1, whereas plastidic picoflagellates accounted for about half this number. Correlations have been evidenced between plastidic and aplastidic micro-organisms within the same size group, suggesting that they belong to a well-defined ecosystem. The highest correlation between total ETS activity and abundance of the considered size groups was observed for nanoflagellates (r = 0.94, n = 22, and r = 0.90, n = 22 for aplastidic and plastidic cells respectively). The importance of the role of nanoflagellates in surface waters, with respect to the overall ETS activity, was supported by results from size fractionation which assigned to the 3-10-mu-m size range a 73.3% contribution to overall ETS activity. Results emphasize analysing global ETS activity of natural samples in order to derive relationships between the different populations present in the sampled water. It is suggested that coupling flow cytometry to the ETS approach should be very helpful in that respect.


Scarpa J, Wada KT, Allen SK (1992) Parthenogenetic Development of Dwarf Surf Clam, Mulinia-Lateralis, Oocytes Treated with Polar Body Suppressing Agents. Invertebrate Reproduction & Development 22 :47-56

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Parthenogenesis following oocyte activation has been observed in a number of marine invertebrates, but the fate of parthenogenesis in bivalve mollusc embryos is unclear. We used the dwarf surf clam, Mulinia lateralis, to examine parthenogenetic development of KCl-activated oocytes using the polar body suppressing agents caffeine and heat or cytochalasin B. Development was followed by epifluorescence microscopy and flow-cytometric analysis using the DNA-specific fluorochrome DAPI. All agents suppressed polar body formation to some degree, putatively increasing the ploidy level and retaining a meiotic centrosome in the zygote ; but the zygotes failed to develop normally. Failure of the zygotes to develop suggests that the meiotic centrosome is incapable of participating in mitosis in bivalves.


Thorsen BK, Enger O, Norland S, Hoff KA (1992) Long-Term Starvation Survival of Yersinia-Ruckeri at Different Salinities Studied by Microscopic and Flow Cytometric Methods. Applied and Environmental Microbiology 58 :1624-1628

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Cultures of three strains of the fish pathogenic bacterium Yersinia ruckeri survived starvation in unsupplemented water for at least 4 months. At salinities of 0 to 20% there were no detectable changes in CFU during the first 3 days of starvation and only a small decrease during the following 4 months, whereas at 35% salinity, the survival potential of the cultures was markedly reduced. These results suggest that Y. ruckeri may survive for long periods in freshwater and brackish environments after an outbreak of enteric redmouth disease. Survival was also examined by use of the direct viable count method, and we show that this method can be combined with flow cytometry for automatic counting of viable bacteria. By flow cytometry, it was shown that genome replication initiated before the onset of starvation was completed, during the initial phase of starvation, and that starved cells could contain up to six genomes per cell.


Vaulot D, Partensky F (1992) Cell-Cycle Distributions of Prochlorophytes in the North-Western Mediterranean-Sea. Deep-Sea Research Part a-Oceanographic Research Papers 39 :727-742

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Natural populations of oceanic prochlorophytes were sampled from the northwestern Mediterranean Sea in winter, stained with the DNA-specific fluorochrome DAPI, and analysed by flow cytometry. DNA histograms exhibited two peaks (G1 and G2 cells, containing one and two genome copies, respectively), separated by a trough of DNA-synthesizing cells (S cells). This suggested a cell cycle with a discrete S phase similar to that observed in eucaryotes or slow-growing procaryotes. Nitrogen and light were the two key environmental factors controlling the in situ cell cycle distributions of this procaryote. When nitrate levels were below 0.4-mu-M or light below 0.1 % of the surface intensity, most of the cells were found in G1, suggesting that they were not actively cycling. Cells arrested in G1 could be induced to cycle into S + G2 by incubating them with added nitrogen. Response was a function of initial nitrate concentration and decreased with depth, indicating that it was modulated by available light. These findings strongly suggest that prochlorophytes, which are one of the key components of the picoplankton community, may grow slowly in nitrogen-depleted waters, but still have the potential to respond quickly to nitrogen pulses.


Viles CL, Sieracki ME (1992) Measurement of Marine Picoplankton Cell-Size by Using a Cooled, Charge-Coupled Device Camera with Image-Analyzed Fluorescence Microscopy. Applied and Environmental Microbiology 58 :584-592

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Accurate measurement of the biomass and size distribution of picoplankton cells (0.2 to 2.0-mu-m) is paramount in characterizing their contribution to the oceanic food web and global biogeochemical cycling. Image-analyzed fluorescence microscopy, usually based on video camera technology, allows detailed measurements of individual cells to be taken. The application of an imaging system employing a cooled, slow-scan charge-coupled device (CCD) camera to automated counting and sizing of individual picoplankton cells from natural marine samples is described. A slow-scan CCD-based camera was compared to a video camera and was superior for detecting and sizing very small, dim particles such as fluorochrome-stained bacteria. Several edge detection methods for accurately measuring picoplankton cells were evaluated. Standard fluorescent microspheres and a Sargasso Sea surface water picoplankton population were used in the evaluation. Global thresholding was inappropriate for these samples. Methods used previously in image analysis of nanoplankton cells (2 to 20-mu-m) also did not work well with the smaller picoplankton cells. A method combining an edge detector and an adaptive edge strength operator worked best for rapidly generating accurate cell sizes. A complete sample analysis of more than 1,000 cells averages about 50 min and yields size, shape, and fluorescence data for each cell. With this system, the entire size range of picoplankton can be counted and measured.