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1.
Bacterium-specific viruses have attracted much interest in aquatic microbial ecology because they have been shown to be about 10 times more abundant than planktonic bacteria. So far most of the studies of interactions of planktonic bacteria and viruses have been done in marine environments, and very little is known about these interactions in lakes. Therefore, we studied phage proliferation in Lake Constance, a large mesotrophic lake in Germany. We enumerated bacteria and quantified the fraction of bacteria with mature intracellular phage particles and the number of free viruses by transmission electron microscopy. Between the end of March and early August 1992, peaks of bacterial abundance were followed in 1 to 2 weeks by peaks in the fraction of bacteria containing visible phage particles (0 to 1.7%) and in the number of free viruses (1 x 10(sup7) to 4 x 10(sup7) ml(sup-1)). We estimated that 1 to 17% +/- 12% of all bacteria were phage infected, implying that phage-induced mortality was <34% +/- 24% of total mortality. A direct comparison between phage-induced mortality, the net decrease of bacterial numbers, and bacterial growth rates indicated that phage-induced mortality accounted for <11% of total bacterial mortality during the phytoplankton spring bloom and 18 to 21% following the bloom. Estimated burst sizes ranged from 21 to 121 phages. Phage production rates of 0.5 x 10(sup6) to 2.5 x 10(sup6) ml(sup-1) day(sup-1) accounted for 70 to 380% of the observed net increase rates of free phages, implying high rates of simultaneous phage decay. The cyclic dynamics between bacteria and phages and the varying size structure of the intracellular mature phage particles suggested that phage infection was important in structuring the bacterial host assemblage during the study period.  相似文献   

2.
Bacterioplankton abundance, [H]thymidine incorporation, CO(2) uptake in the dark, and fractionated primary production were measured on several occasions between June and August 1982 in eutrophic Lake Norrviken, Sweden. Bacterioplankton abundance and carbon biomass ranged from 0.5 x 10 to 2.4 x 10 cells liter and 7 to 47 mug of C liter, respectively. The average bacterial cell volume was 0.185 mum. [H]thymidine incorporation into cold-trichloroacetic acid-insoluble material ranged from 12 x 10 to 200 x 10 mol liter h. Bacterial carbon production rates were estimated to be 0.2 to 7.1 mug of C liter h. Bacterial production estimates from [H]thymidine incorporation and CO(2) uptake in the dark agreed when activity was high but diverged when activity was low and when blue-green algae (cyanobacteria) dominated the phytoplankton. Size fractionation indicated negligible uptake of [H]thymidine in the >3-mum fraction during a chrysophycean bloom in early June. We found that >50% of the H activity was in the >3-mum fraction in late August; this phenomenon was most likely due to Microcystis spp., their associated bacteria, or both. Over 60% of the CO(2) uptake in the dark was attributed to algae on each sampling occasion. Algal exudate was an important carbon source for planktonic bacteria. Bacterial production was roughly 50% of primary production.  相似文献   

3.
During three periods of 16 to 25 days, bacterioplankton production, bacterial cell volume, chlorophyll a, CO2 assimilation, and particulate organic carbon were measured in enclosures situated in the eutrophic estuary Roskilde Fjord, Denmark. The enclosures were manipulated with respect to sediment contact and contents of inorganic nutrients, planktivorous fish, and suspension-feeding bivalves. Nutrient enrichment, the presence of suspension feeders, and sediment contact induced pronounced changes in bacterial production, as well as minor changes in bacterial cell volume; however, these effects seemed to be indirect, transmitted via phytoplankton. Bacterial production, measured as [3H]thymidine incorporation, closely followed changes in phytoplankton biomass and production, with time lags of 5 to 10 days. Good correlations of mean bacterioplankton production to chlorophyll a concentration and CO2 assimilation suggested phytoplankton to be the dominating source of bacterial substrate, apparently independent of nutrient stress. Zooplankton >140 μm, bivalves, and sediment seemed to provide insignificant, if any, substrate for bacterioplankton, and benthic suspension feeders seemed not to act as direct competitors for dissolved organic carbon. The bacterioplankton mean cell volume, measured by image analysis, changed seasonally, with the smallest cells during the summer. Within each period, the bacterial cell volume correlated positively to growth rate and negatively to temperature.  相似文献   

4.
Production and Consumption of Hydrogen in a Eutrophic Lake   总被引:1,自引:4,他引:1       下载免费PDF全文
The vertical distribution of hydrogen was measured in the Loclat, a eutrophic and holomictic lake near Neuchâtel, Switzerland, before and during summer stratification. H2 concentrations decreased with depth in the anaerobic hypolimnion and were often below the detection limit (2.5 nl of H2 liter−1) in the water adjacent to the lake sediment. H2 was apparently not released from the lake sediment. The highest H2 concentrations (>4 μl of H2 liter−1) were observed in the aerobic water of the epilimnion and metalimnion. There, the H2 concentrations changed with time, indicating a turnover of H2. The H2 production processes could not be studied in the laboratory since incubation of water samples in light or darkness did not result in H2 production but rather always in H2 consumption. The possible role of cyanobacteria and algae for H2 production is discussed. Aerobic or anaerobic H2 consumption activities were observed at all depths of the water column, with highest activities in the hypolimnion. Aerobic H2 consumption activity was insensitive to azide inhibition, but sensitive to heat, mercuric chloride, or cyanide. It was restricted to a particle fraction of 0.2 to 3.0 μm in size, so that it must be due to single bacterial cells. Aerobic hydrogen bacteria, on the other hand, occurred in clusters of >3.0 μm. Therefore, the hydrogen bacteria could not have caused the H2 consumption in lake water. The aerobic H2 consumption activity followed Michaelis-Menten kinetics, with a Km of 67 nM H2. This is an exceptionally low value compared with Km values of hydrogenases in hydrogen bacteria and other species, but is similar to that for H2-decomposing abiontic soil hydrogenases.  相似文献   

5.
Experiments were conducted to determine whether production of heterotrophic bacterioplankton in a small meso-eutrophic lake was influenced by the dissolved inorganic phosphorus (DIP) supply. DIP may indirectly limit bacterial production by limiting phytoplankton, which in turn may limit the carbon available to bacteria. Direct DIP limitation of bacteria occurs where the availability of DIP for bacteria is insufficient to maintain growth. This work examined direct DIP limitation of bacteria by removing phytoplankton and incubating flasks with or without added P in the dark. Bacterial production was measured via the rate of incorporation of [3H]thymidine ([3H]TdR) into DNA. Bacterial abundance was followed with epifluorescent direct counts. Rates of [3H]TdR incorporation were significantly greater in flasks with added DIP, and changes in cell abundances generally paralleled increases in [3H]TdR incorporation. Even very small additions of P (0.05 μM) were sufficient to stimulate production. DIP addition to whole lakewater also stimulated [3H]TdR incorporation relative to that in zero-addition controls, but there was not a concurrent increase in bacterial cell numbers. The stimulation of [3H]TdR incorporation after DIP addition to whole lakewater was significantly less than the stimulation due to DIP addition to 1-μm-pore-size-filtered lakewater. In this study, addition of DIP caused as much as an eightfold stimulation of [3H]TdR incorporation.  相似文献   

6.
Inhibitors of eucaryotes (cycloheximide and amphotericin B) and procaryotes (penicillin and chloramphenicol) were used to estimate bacterivory and bacterial production in a eutrophic lake. Bacterial production appeared to be slightly greater than protozoan grazing in the aerobic waters of Lake Oglethorpe. Use of penicillin and cycloheximide yielded inconsistent results in anaerobic water and in aerobic water when bacterial production was low. Production measured by inhibiting eucaryotes with cycloheximide did not always agree with [3H]thymidine estimates or differential filtration methods. Laboratory experiments showed that several common freshwater protozoans continued to swim and ingest bacterium-size latex beads in the presence of the eucaryote inhibitor. Penicillin also affected grazing rates of some ciliates. We recommend that caution and a corroborating method be used when estimating ecologically important parameters with specific inhibitors.  相似文献   

7.
Bacterioplankton from a meso-eutrophic dam reservoir was size fractionated to reduce (<0.8-μm treatment) or enhance (<5-μm treatment) protistan grazing and then incubated in situ for 96 h in dialysis bags. Time course samples were taken from the bags and the reservoir to estimate bacterial abundance, mean cell volume, production, protistan grazing, viral abundance, and frequency of visibly infected cells. Shifts in bacterial community composition (BCC) were examined by denaturing gradient gel electrophoresis (DGGE), cloning and sequencing of 16S rDNA genes from the different treatments, and fluorescence in situ hybridization (FISH) with previously employed and newly designed oligonucleotide probes. Changes in bacterioplankton characteristics were clearly linked to changes in mortality rates. In the reservoir, where bacterial production about equaled protist grazing and viral mortality, community characteristics were nearly invariant. In the “grazer-free” (0.8-μm-filtered) treatment, subject only to a relatively low mortality rate (~17% day−1) from viral lysis, bacteria increased markedly in concentration. While the mean bacterial cell volume was invariant, DGGE indicated a shift in BCC and FISH revealed an increase in the proportion of one lineage within the beta proteobacteria. In the grazing-enhanced treatment (5-μm filtrate), grazing mortality was ~200% and viral lysis resulted in mortality of 30% of daily production. Cell concentrations declined, and grazing-resistant flocs and filaments eventually dominated the biomass, together accounting for >80% of the total bacteria by the end of the experiment. Once again, BCC changed strongly and a significant fraction of the large filaments was detected using a FISH probe targeted to members of the Flectobacillus lineage. Shifts of BCC were also reflected in DGGE patterns and in the increases in the relative importance of both beta proteobacteria and members of the Cytophaga-Flavobacterium cluster, which consistently formed different parts of the bacterial flocs. Viral concentrations and frequencies of infected cells were highly significantly correlated with grazing rates, suggesting that protistan grazing may stimulate viral activity.  相似文献   

8.
Application of eucaryote inhibitors to the estimation of production and grazing mortality of bacterioplankton was evaluated. Exposure to a range of concentrations of thiram, cycloheximide, and neutral red (0.4 to 210, 36 to 1,777, 4 to 346 μM, respectively) was 98 to 100% effective at inhibiting growth of a chrysomonad in culture. Exposure to colchicine and griseofulvin (50 to 1,000 μM for both) yielded only 24 to 94 and 53 to 79% inhibition, respectively. Exposures to thiram, neutral red, and griseofulvin were 90 to 100% effective at inhibiting growth in culture of a ciliate, Cyclidium sp., and the responses to colchicine and cycloheximide were variable (64 to 100 and 0 to 100% inhibition, respectively). Thiram and neutral red inhibited field populations of nanozooplankton more effectively than cycloheximide and colchicine. Direct effects of eucaryote inhibitors on growing cultures of bacterioplankton varied with parameters measured and duration of exposure. After 3-day exposures, specific growth rates and “instantaneous” heterotrophic potential ([14C]glucose uptake) were not consistently affected, but biosynthetic activity (RNA and DNA syntheses) was depressed. The degree of inhibition of isolates and field populations of phytoplankton depended upon type of inhibitor and phytoplankton species. In field experiments, it was possible to calculate rates of bacterioplankton production and grazing mortality for only 16 of 29 inhibitor experiments and for 4 of 10 size fractionation experiments. Bacterioplankton production and mortality estimates varied greatly with the eucaryote inhibitor used, and those derived from inhibition techniques were substantially different from those derived from fractionation techniques. The poor performances of both techniques are attributed to the following: (i) effects of inhibitors on phytoplankton, (ii) indirect effects of the inhibitors on bacterioplankton, and (iii) insufficient separation of grazers from prey by filtration techniques. Because of the inconsistent results obtained in this investigation, we strongly recommend exercising caution in the application of inhibitor techniques to ecological problems, especially in phototrophically dominated systems.  相似文献   

9.
Estimates were made of the biomass and production of heterotrophic bacteria in the epilimnion of Lake Mendota, Wis. Cell counts were done with epifluorescence microscopy and varied from 3 × 105 bacteria per ml in winter to 3 × 106 bacteria per ml in summer. Cell volumes were measured in scanning electron micrographs. The average cell volume was 0.159 μm3. Annual variations and depth distribution were studied. Production was estimated from the frequency of dividing cells and from dark radioactive sulfate uptake. Annual productivity and daily average productivity were very close with both methods: 107 to 205 g of C per m2 per year for sulfate and 89 to 117 g of C per m2 per year for frequency of dividing cells. Zooplankton feeding removed 2 to 10% of the bacterial net production annually. When compared with biomass changes and losses due to zooplankton feeding, production values were very high. Therefore, it was suggested that other loss factors have to be more important than zooplankton feeding in controlling the bacterial population. Bacterial heterotrophic production was about 50% of gross primary production.  相似文献   

10.
The spring development of both phytoplankton and bacterioplankton was investigated between 18 April and 7 May 1983 in mesotrophic Lake Erken, Sweden. By using the lake as a batch culture, our aim was to estimate, via different methods, the production of phytoplankton and bacterioplankton in the lake and to compare these production estimates with the actual increase in phytoplankton and bacterioplankton biomass. The average water temperature was 3.5°C. Of the phytoplankton biomass, >90% was the diatom Stephanodiscus hantzchii var. pusillus, by the peak of the bloom. The 14C and O2 methods of estimating primary production gave equivalent results (r = 0.999) with a photosynthetic quotient of 1.63. The theoretical photosynthetic quotient predicted from the C/NO3 N assimilation ratio was 1.57. The total integrated incorporation of [14C]bicarbonate into particulate material (>1 μm) was similar to the increase in phytoplankton carbon determined from cell counts. Bacterioplankton increased from 0.5 × 109 to 1.52 × 109 cells liter−1 (~0.5 μg of C liter−1 day−1). Estimates of bacterioplankton production from rates of [3H]thymidine incorporation were ca. 1.2 to 1.7 μg of C liter−1 day−1. Bacterial respiration, measured by a high-precision Winkler technique, was estimated as 4.8 μg of C liter−1 day−1, indicating a bacterial growth yield of 25%. The bulk of the bacterioplankton production was accounted for by algal extracellular products. Gross bacterioplankton production (production plus respiration) was 20% of gross primary production, per square meter of surface area. We found no indication that bacterioplankton production was underestimated by the [3H]thymidine incorporation method.  相似文献   

11.
Bacterioplankton abundance and production were followed during one decade (1991–2001) in the hypertrophic and steeply stratified small Lake Verevi (Estonia). The lake is generally dimictic. However, a partly meromictic status could be formed in specific meteorological conditions as occurred in springs of 2000 and 2001. The abundance of bacteria in Lake Verevi is highly variable (0.70 to 22 × 106 cells ml−1) and generally the highest in anoxic hypolimnetic water. In 2000–2001, the bacterial abundance in the hypolimnion increased probably due to meromixis. During a productive season, heterotrophic bacteria were able to consume about 10–40% of primary production in the epilimnion. Our study showed that bacterioplankton in the epilimnion was top-down controlled by predators, while in metalimnion bacteria were dependent on energy and carbon sources (bottom-up regulated). Below the thermocline hypolimnetic bacteria mineralized organic matter what led to the depletion of oxygen and created anoxic hypolimnion where rich mineral nutrient and sulphide concentrations coexisted with high bacterial numbers.  相似文献   

12.
The distribution and abundance of larval chironomids in Lake Hayes were studied from December 1973 to March 1975. The mean annual production of the two dominant species, Chironomus zealandicus and Chironomus sp. a, was 29.2 g m−2 dry weight which is approximately 4.3 % of the average annual phytoplankton production in the lake. A high annual P/B ratio of 18.5 is consistent with the multivoltine life cycle of C. zealandicus. Larval chironomid production in the second summer when Anabaena blooms were absent was only one quarter of that in the first summer and is consistent with the hypothesis that the production of benthic chironomids in Lake Hayes is closely linked to that of the phytoplankton through the sedimentation of autochthonous organic matter.  相似文献   

13.
Seasonal Variation of Virioplankton in a Eutrophic Shallow Lake   总被引:5,自引:0,他引:5  
Lake Donghu is a typical eutrophic freshwater lake in which high abundance of planktonic viruses was recently revealed. In this study, seasonal variation of planktonic viruses were observed at three different trophic sites, hypertrophic, eutrophic, and mesotrophic regions, and the correlation between their abundances and other aquatic environmental components, such as bacterioplankton, chlorophyll a, burst size, pH, dissolved oxygen, and temperature, was analyzed for the period of an year. Virioplankton abundance detected by transmission electron microscope (TEM) ranged from 5.48 × 108 to 2.04 × 109 ml−1 in all the sites throughout the study, and the high abundances and seasonal variations of planktonic viruses were related to the trophic status at the sampled sites in Lake Donghu. Their annual mean abundances were, the highest at the hypertrophic site (1.23×109 ml−1), medium at the eutrophic site (1.19×109 ml−1), and the lowest at the mesotrophic site (1.02×109 ml−1). The VBR (virus-to-bacteria ratio) values were high, ranging from 49 to 56 on average at the three sampled sites. The data suggested that the high viral abundance and high VBR values might be associated with high density of phytoplankton including algae and cyanobacteria in this eutrophic shallow lake, and that planktonic viruses are important members of freshwater ecosystems.  相似文献   

14.
Annual Patterns in Bacterioplankton Community Variability in a Humic Lake   总被引:4,自引:0,他引:4  
Bacterioplankton community composition (BCC) was monitored in a shallow humic lake in northern Wisconsin, USA, over 3 years using automated ribosomal intergenic spacer analysis (ARISA). Comparison of ARISA profiles of bacterial communities over time indicated that BCC was highly variable on a seasonal and annual scale. Nonmetric multidimensional scaling (MDS) analysis indicated little similarity in BCC from year to year. Nevertheless, annual patterns in bacterioplankton community diversity were observed. Trends in bacterioplankton community diversity were correlated to annual patterns in community succession observed for phytoplankton and zooplankton populations, consistent with the notion that food web interactions affect bacterioplankton community structure in this humic lake. Bacterioplankton communities experience a dramatic drop in richness and abundance each year in early summer, concurrent with an increase in the abundance of both mixotrophic and heterotrophic flagellates. A second drop in richness, but not abundance, is observed each year in late summer, coinciding with an intense bloom of the nonphagotrophic dinoflagellate Peridinium limbatum. A relationship between bacterial community composition, size, and abundance and the population dynamics of Daphnia was also observed. The noted synchrony between these major population and species shifts suggests that linkages across trophic levels play a role in determining the annual time course of events for the microbial and metazoan components of the plankton.  相似文献   

15.
Variability in Microbiological Data from a Stratified Eutrophic Lake   总被引:1,自引:0,他引:1  
A survey of a stratified eutrophic lake was undertaken to determine the degree of variability in direct counts of bacteria, electron transport system activity, ATP concentration, chlorophyll a concentration and chemiluminescence, in the water column and the sediment. Heterogeneity in the horizontal and vertical dimension was studied in detail and the scale of variability was compared with within-sample and between-sample errors, and with seasonal fluctuations. Variability was greater in the sediment samples, and the coefficient of variation of samples taken at a single site was often as large as that between sites in a transect across the lake. Although this was not an exhaustive survey, the values provided should allow rough estimates to be made of the number of samples required to achieve a given level of precision in future investigations.  相似文献   

16.
Differences in enzymatic hydrolysis of dissolved organic phosphorus and subsequent phosphorus uptake were compared by using dual-labeled (γ-32P and 2-3H) ATP in oligotrophic Lake Michigan and a moderately eutrophic lake in southeastern Michigan. More than 50% of the phosphate that was hydrolyzed was immediately taken up into bacterium-sized particles in the eutrophic lake and at a near-shore site in Lake Michigan. Less than 50% of the hydrolyzed phosphate was taken up into bacterium-sized particles at an offshore site in Lake Michigan. It is hypothesized that differences in size-fractionated uptake were the result of greater phosphorus utilization capacity in bacteria in habitats where loading of organic carbon is greater. Substantial isotope dilution of labeled phosphate uptake by unlabeled phosphate occurred, which implied that the phosphate was hydrolyzed extracellularly in both systems. Comparable nucleotidase activities were measured in the eutrophic lake and Lake Michigan, but the significance of the phosphate regenerated relative to particulate phosphorus pools was an order of magnitude greater in Lake Michigan. Seventy percent of the nucleotidase activity was inhibited by 100 μM phosphate in the eutrophic lake, which suggests that most hydrolysis was by phosphatase. Therefore, nucleotidase activity may be more important to phosphorus regeneration in oligotrophic habitats than phosphatase activity.  相似文献   

17.
The relative importance of viral lysis and bacterivory as causes of bacterial mortality were estimated. A laboratory experiment was carried out to check the kind of control that viruses could exert over the bacterial assemblage in a non-steady-state situation. Virus-like particles (VLP) were determined by using three methods of counting (DAPI [4′,6-diamidino-2-phenylindole] staining, YOPRO staining, and transmission electron microscopy). Virus counts increased from the beginning until the end of the experiment. However, different methods produced significantly different results. DAPI-stained VLP yielded the lowest numbers, while YOPRO-stained VLP yielded the highest numbers. Bacteria reached the maximal abundance at 122 h (3 × 107 bacteria ml−1), after the peak of chlorophyll a (80 μg liter−1). Phototrophic nanoflagellates followed the same pattern as for chlorophyll a. Heterotrophic nanoflagellates showed oscillations in abundance throughout the experiment. The specific bacterial growth rate increased until 168 h (2.6 day−1). The bacterivory rate reached the maximal value at 96 hours (0.9 day−1). Bacterial mortality due to viral infection was measured by using two approaches: measuring the percentage of visibly infected bacteria (%VIB) and measuring the viral decay rates (VDR), which were estimated with cyanide. The %VIB was always lower than 1% during the experiment. VDR were used to estimate viral production. Viral production increased 1 order of magnitude during the experiment (from 106 to 107 VLP ml−1 h−1). The percentage of heterotrophic bacterial production consumed by bacterivores was higher than 60% during the first 4 days of the experiment; afterwards, this percentage was lower than 10%. The percentage of heterotrophic bacterial production lysed by viruses as assessed by the VDR reached the highest values at the beginning (100%) and at the end (50%) of the experiment. Comparing both sources of mortality at each stage of the bloom, bacterivory was found to be higher than viral lysis at days 2 and 4, and viral lysis was higher than bacterivory at days 7 and 9. A balance between bacterial losses and bacterial production was calculated for each sampling interval. At intervals of 0 to 2 and 2 to 4 days, viral lysis and bacterivory accounted for all the bacterial losses. At intervals of 4 to 7 and 7 to 9 days, bacterial losses were not balanced by the sources of mortality measured. At these time points, bacterial abundance was about 20 times higher than the expected value if viral lysis and bacterivory had been the only factors causing bacterial mortality. In conclusion, mortality caused by viruses can be more important than bacterivory under non-steady-state conditions.  相似文献   

18.
Monoclonal antibodies and epifluorescence microscopy were used to determine the depth distribution of two indigenous bacterial populations in the stratified Lake Plußsee and characterize their life strategies. Populations of Comamonas acidovorans PX54 showed a depth distribution with maximum abundances in the oxic epilimnion, whereas Aeromonas hydrophila PU7718 showed a depth distribution with maximum abundances in the anoxic thermocline layer (metalimnion), i.e., in the water layer with the highest microbial activity. Resistance of PX54 to protist grazing and high metabolic versatility and growth rate of PU7718 were the most important life strategy traits for explaining the depth distribution of the two bacterial populations. Maximum abundance of PX54 was 16,000 cells per ml, and maximum abundance of PU7718 was 20,000 cells per ml. Determination of bacterial productivity in dilution cultures with different-size fractions of dissolved organic matter (DOM) from lake water indicates that low-molecular-weight (LMW) DOM is less bioreactive than total DOM (TDOM). The abundance and growth rate of PU7718 were highest in the TDOM fractions, whereas those of PX54 were highest in the LMW DOM fraction, demonstrating that PX54 can grow well on the less bioreactive DOM fraction. We estimated that 13 to 24% of the entire bacterial community and 14% of PU7718 were removed by viral lysis, whereas no significant effect of viral lysis on PX54 could be detected. Growth rates of PX54 (0.11 to 0.13 h−1) were higher than those of the entire bacterial community (0.04 to 0.08 h−1) but lower than those of PU7718 (0.26 to 0.31 h−1). In undiluted cultures, the growth rates were significantly lower, pointing to density effects such as resource limitation or antibiosis, and the effects were stronger for PU7718 and the entire bacterial community than for PX54. Life strategy characterizations based on data from literature and this study revealed that the fast-growing and metabolically versatile A. hydrophila PU7718 is an r-strategist or opportunistic population in Lake Plußsee, whereas the grazing-resistant C. acidovorans PX54 is rather a K-strategist or equilibrium population.  相似文献   

19.
Viral and Bacterioplankton Dynamics in Two Lakes with Different Humic Contents   总被引:10,自引:0,他引:10  
Viral and bacterioplankton dynamics were investigated, together with the temporal variation of phage-infected bacterioplankton in two oligotrophic lakes, one humic and the other clearwater. Bacterial abundance was significantly higher in the humic lake, while the abundance of virus-like particles (VLP) was significantly higher in the clearwater lake. There were no differences in either the frequency of infected bacterial cells (FIC), or in burst size between the lakes. Because of the higher bacterial abundance in the humic lake, a larger number of bacteria were lyzed in this lake. FIC showed large seasonal changes, varying between 9 and 43%, which covers almost the entire range of previously published data from both lacustrine and marine environments. The temporal changes in VLP abundance and FIC were slow in both the humic and clearwater lakes. The burst size was low in both lakes (average value, nine in each case), probably because of the oligotrophic status of the lakes. The chlorophyll a concentrations were higher and positively correlated with VLP numbers in the clearwater lake, indicating that a significant proportion of the viruses in this lake may be phytoplankton viruses.  相似文献   

20.
Dilution culture experiments were conducted in western North Pacific coastal regions to determine growth and grazing mortality rates of bacterial phylogenetic groups (α-, β-, and γ-proteobacteria and the Cytophaga-Flavobacter cluster) detected by fluorescent in situ hybridization. Growth rates varied greatly (1.2- to 4.0-fold) among different groups, and they were related to environmental variables (chlorophyll a concentrations and temperature) in a group-specific fashion. Growth rates of α-proteobacteria, the most abundant group in all the samples examined, were generally lower than those of less abundant groups, including the Cytophaga-Flavobacter cluster and γ-proteobacteria. Grazing mortality rates and mean cell volumes varied little among different groups. These results provide insights into factors that affect distributions of different groups, but growth and grazing mortality alone did not fully explain bacterial community compositions at a broad phylogenetic level.  相似文献   

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