scholarly journals Viral Lysis and Bacterivory during a Phytoplankton Bloom in a Coastal Water Microcosm

1999 ◽  
Vol 65 (5) ◽  
pp. 1949-1958 ◽  
Author(s):  
Núria Guixa-Boixereu ◽  
Kristine Lysnes ◽  
Carlos Pedrós-Alió
Keyword(s):  
Steady State ◽  
Bacterial Production ◽  
Phytoplankton Bloom ◽  
Decay Rates ◽  
Heterotrophic Nanoflagellates ◽  
Viral Production ◽  
Viral Lysis ◽  
Bacterial Growth Rate ◽  
Bacterial Assemblage ◽  
Bacterial Mortality

ABSTRACT 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 chlorophylla. 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−1h−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.

scholarly journals Enhanced viral production and virus-mediated mortality of bacterioplankton in a natural iron-fertilized bloom event above the Kerguelen Plateau

2014 ◽  
Vol 11 (23) ◽  
pp. 6841-6853 ◽  
Author(s):  
A. Malits ◽  
U. Christaki ◽  
I. Obernosterer ◽  
M. G. Weinbauer
Keyword(s):  
Food Web ◽  
Phytoplankton Bloom ◽  
Austral Summer ◽  
Heterotrophic Nanoflagellates ◽  
Viral Production ◽  
Kerguelen Plateau ◽  
Viral Lysis ◽  
Iron Fertilization ◽  
Natural Iron ◽  
Infected Cells

Abstract. Above the Kerguelen Plateau in the Southern Ocean natural iron fertilization sustains a large phytoplankton bloom over 3 months during austral summer. During the KEOPS1 project (KErguelen Ocean and Plateau compared Study1) we sampled this phytoplankton bloom during its declining phase along with the surrounding high-nutrient–low-chlorophyll (HNLC) waters to study the effect of natural iron fertilization on the role of viruses in the microbial food web. Bacterial and viral abundances were 1.7 and 2.1 times, respectively, higher within the bloom than in HNLC waters. Viral production and virus-mediated mortality of bacterioplankton were 4.1 and 4.9 times, respectively, higher in the bloom, while the fraction of infected cells (FIC) and the fraction of lysogenic cells (FLC) showed no significant differences between environments. The present study suggests viruses to be more important for bacterial mortality within the bloom and dominate over grazing of heterotrophic nanoflagellates (HNFs) during the late bloom phase. As a consequence, at least at a late bloom stage, viral lysis shunts part of the photosynthetically fixed carbon in iron-fertilized regions into the dissolved organic matter (DOM) pool with potentially less particulate organic carbon transferred to larger members of the food web or exported.

scholarly journals Diel Variation of Viral Production in a Coastal Subtropical Marine System

Diversity ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 426
Author(s):  
Pei-Chi Ho ◽  
Gwo-Ching Gong ◽  
Chih-Hao Hsieh ◽  
Patrichka Wei-Yi Chen ◽  
An-Yi Tsai
Keyword(s):  
Linear Regression ◽  
Coastal Region ◽  
Cell Types ◽  
Linear Regression Method ◽  
Diel Variation ◽  
Viral Production ◽  
Viral Lysis ◽  
Bacterial Mortality ◽  
Marine System ◽  
Classical Linear Regression

Viral production (VP) and bacterial mortality by viral lysis critically influence the production and mortality of aquatic bacteria. Although bacterial production, mortality by viral lysis, and viral density have been found to exhibit diel variations, the diel change in viral production has rarely been investigated. In this study, we conducted two diel dilution incubation experiments in a semi-enclosed, nutrient-rich coastal region in northeastern Taiwan to estimate the diel viral production and the mortality by viral lysis. We also compared two methods (linear regression between viral density and time versus arithmetic mean of VP during incubation) of estimating viral production. We found that viral production estimated by linear regression and bacterial mortality by viral lysis were higher during the daytime than during the nighttime. A possible explanation for the high viral production at daytime is that the bacterial community was composed of cell types with higher burst sizes at daytime. We further argued that the classical linear regression method can be used only when viral density significantly linearly increases with time, which does not always occur in dilution incubations. This study offered observations of diel variation in viral dynamics and discussed the methods estimating viral production in a marine environment.

scholarly journals Quantifying the structure of the mesopelagic microbial loop from observed depth profiles of bacteria and protozoa

2004 ◽  
Vol 1 (1) ◽  
pp. 413-428 ◽  
Author(s):  
T. Tanaka ◽  
F. Rassoulzadegan ◽  
T. F. Thingstad
Keyword(s):  
Steady State ◽  
Bacterial Production ◽  
Microbial Loop ◽  
Heterotrophic Nanoflagellates ◽  
Similar Amount ◽  
Chain Model ◽  
Trophic Link ◽  
Depth Profiles ◽  
Food Chain Model ◽  
Northwestern Mediterranean

Abstract. t is widely recognized that organic carbon exported to the ocean aphotic layer is significantly consumed by heterotrophic organisms such as bacteria and zooplankton in the mesopelagic layer. However, very little is known for the trophic link between bacteria and zooplankton or the structure of the microbial loop in this layer. In the northwestern Mediterranean, recent studies have shown that viruses, bacteria, heterotrophic nanoflagellates, and ciliates distribute down to 2000 m with group-specific depth-dependent decreases, and that bacterial production decreases with depth down to 1000 m. Here we show that such data can be analyzed using a simple steady-state food chain model to quantify the carbon flow from bacteria to zooplankton over the mesopelagic layer. The model indicates that a similar amount of bacterial production is allocated to viruses and heterotrophic nanoflagellates, and that heterotrophic nanoflagellates are the important remineralizers.

scholarly journals Microbial food web dynamics during spring phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)

2014 ◽  
Vol 11 (5) ◽  
pp. 6985-7028 ◽  
Author(s):  
U. Christaki ◽  
D. Lefèvre ◽  
C. Georges ◽  
J. Colombet ◽  
P. Catala ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Food Web ◽  
Bacterial Production ◽  
Microbial Food Web ◽  
Heterotrophic Nanoflagellates ◽  
Bacterial Respiration ◽  
Viral Production ◽  
Phytoplankton Blooms ◽  
Food Web Dynamics ◽  
Heterotrophic Production

Abstract. Microbial food web dynamics were determined during the onset of several spring phytoplankton blooms induced by natural iron fertilization off Kerguelen Island in the Southern Ocean (KEOPS2). The abundances of heterotrophic bacteria and heterotrophic nanoflagellates, bacterial heterotrophic production, bacterial respiration, and bacterial growth efficiency, were consistently higher in surface waters of the iron-fertilized sites than at the reference site in HNLC (high nutrient low chlorophyll) waters. The abundance of viral like particles remained unchanged, but viral production increased by a factor of 6 in iron-fertilized waters. Bacterial heterotrophic production was significantly related to heterotrophic nanoflagellate abundance and viral production across all sites, with bacterial production explaining about 70 and 85%, respectively, of the variance of each in the mixed layer (ML). Estimated rates of grazing and viral lysis, however, indicated that heterotrophic nanoflagellates accounted for a substantially higher loss of bacterial production (50%) than viruses (11%). Combining these results with rates of primary production and export determined for the study area, a budget for the flow of carbon through the microbial food web and higher levels during the early (KEOPS2) and the late phase (KEOPS1) of the Kerguelen bloom is provided.

scholarly journals Microbial food web dynamics during spring phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)

2014 ◽  
Vol 11 (23) ◽  
pp. 6739-6753 ◽  
Author(s):  
U. Christaki ◽  
D. Lefèvre ◽  
C. Georges ◽  
J. Colombet ◽  
P. Catala ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Food Web ◽  
Bacterial Production ◽  
Trophic Levels ◽  
Microbial Food Web ◽  
Heterotrophic Nanoflagellates ◽  
Viral Production ◽  
Phytoplankton Blooms ◽  
Food Web Dynamics ◽  
Heterotrophic Production

Abstract. Microbial food web dynamics were determined during the onset of several spring phytoplankton blooms induced by natural iron fertilization off Kerguelen Island in the Southern Ocean (KEOPS2). The abundances of heterotrophic bacteria and heterotrophic nanoflagellates, bacterial heterotrophic production, bacterial respiration, and bacterial growth efficiency, were consistently higher in surface waters of the iron-fertilized sites than at the reference site in HNLC (high nutrient low chlorophyll) waters. The abundance of virus-like particles remained unchanged, but viral production increased by a factor of 6 in iron-fertilized waters. Bacterial heterotrophic production was significantly related to heterotrophic nanoflagellate abundance and viral production across all sites, with bacterial production explaining about 70 and 85%, respectively, of the variance of each in the mixed layer (ML). Estimated rates of grazing and viral lysis, however, indicated that heterotrophic nanoflagellates accounted for a substantially higher loss of bacterial production (50%) than viruses (11%). Combining these results with rates of primary production and export determined for the study area, a budget for the flow of carbon through the microbial food web and higher trophic levels during the early (KEOPS2) and the late phase (KEOPS1) of the Kerguelen bloom is provided.

scholarly journals Significance of Viral Lysis and Flagellate Grazing as Factors Controlling Bacterioplankton Production in a Eutrophic Lake

1998 ◽  
Vol 64 (2) ◽  
pp. 431-438 ◽  
Author(s):  
Markus G. Weinbauer ◽  
Manfred G. Höfle
Keyword(s):  
Organic Matter ◽  
Bacterial Production ◽  
Eutrophic Lake ◽  
Bacterial Cells ◽  
Viral Lysis ◽  
Thin Sections ◽  
Bacterial Mortality ◽  
Bacterioplankton Production ◽  
Transmission Electron ◽  
Heterotrophic Nanoflagellate

ABSTRACT The effects of viral lysis and heterotrophic nanoflagellate (HNF) grazing on bacterial mortality were estimated in a eutrophic lake (Lake Plußsee in northern Germany) which was separated by a steep temperature and oxygen gradient into a warm and oxic epilimnion and a cold and anoxic hypolimnion. Two transmission electron microscopy-based methods (whole-cell examination and thin sections) were used to determine the frequency of visibly infected cells, and a model was used to estimate bacterial mortality due to viral lysis. Examination of thin sections also showed that between 20.2 and 29.2% (average, 26.1%) of the bacterial cells were empty (ghosts) and thus could not contribute to viral production. The most important finding was that the mechanism for regulating bacterial production shifted with depth from grazing control in the epilimnion to control due to viral lysis in the hypolimnion. We estimated that in the epilimnion viral lysis accounted on average for 8.4 to 41.8% of the summed mortality (calculated by determining the sum of the mortalities due to lysis and grazing), compared to 51.3 to 91.0% of the summed mortality in the metalimninon and 88.5 to 94.2% of the summed mortality in the hypolimnion. Estimates of summed mortality values indicated that bacterial production was controlled completely or almost completely in the epilimnion (summed mortality, 66.6 to 128.5%) and the hypolimnion (summed mortality, 43.4 to 103.3%), whereas in the metalimnion viral lysis and HNF grazing were not sufficient to control bacterial production (summed mortality, 22.4 to 56.7%). The estimated contribution of organic matter released by viral lysis of cells into the pool of dissolved organic matter (DOM) was low; however, since cell lysis products are very likely labile compared to the bulk DOM, they might stimulate bacterial production. The high mortality of bacterioplankton due to viral lysis in anoxic water indicates that a significant portion of bacterial production in the metalimnion and hypolimnion is cycled in the bacterium-virus-DOM loop. This finding has major implications for the fate and cycling of organic nutrients in lakes.

scholarly journals Enhanced viral production and virus-mediated mortality of bacterioplankton in a natural iron-fertilized bloom event above the Kerguelen Plateau

2014 ◽  
Vol 11 (7) ◽  
pp. 10827-10862 ◽  
Author(s):  
A. Malits ◽  
U. Christaki ◽  
I. Obernosterer ◽  
M. G. Weinbauer
Keyword(s):  
Food Web ◽  
Phytoplankton Bloom ◽  
Austral Summer ◽  
Viral Production ◽  
Kerguelen Plateau ◽  
Viral Lysis ◽  
Iron Fertilization ◽  
Protozoan Grazing ◽  
Natural Iron ◽  
Infected Cells

Abstract. Above the Kerguelen Plateau in the Southern Ocean natural iron fertilization sustains a large phytoplankton bloom over three months during austral summer. During the KEOPS1 project (KErguelen Ocean and Plateau compared Study1) we sampled this phytoplankton bloom during its declining phase along with the surrounding HNLC waters to study the effect of natural iron fertilization on the role of viruses in the microbial food web. Bacterial and viral abundances were 1.7 and 2.1 times, respectively, higher within the bloom than in HNLC waters. Viral production and virus-mediated mortality of bacterioplankton was 4.1 and 4.9 times, respectively, higher in the bloom, while the fraction of infected cells (FIC) and the fraction of lysogenic cells (FLC) showed no significant differences between environments. The present study suggests viruses to be more important for bacterial mortality within the bloom and dominate over protozoan grazing during the late bloom phase. As a consequence, at least at a late bloom stage, viral lysis shunts part of the photosynthetically fixed carbon in iron-fertilized regions into the dissolved organic matter (DOM) pool with potentially less particulate organic carbon transfered to larger members of the food web or exported.

scholarly journals Analyzing the trophic link between the mesopelagic microbial loop and zooplankton from observed depth profiles of bacteria and protozoa

2005 ◽  
Vol 2 (1) ◽  
pp. 9-13 ◽  
Author(s):  
T. Tanaka ◽  
F. Rassoulzadegan ◽  
T. F. Thingstad
Keyword(s):  
Bacterial Production ◽  
Microbial Loop ◽  
Trophic Levels ◽  
Heterotrophic Nanoflagellates ◽  
Chain Model ◽  
Bacterial Mortality ◽  
Trophic Link ◽  
Depth Profiles ◽  
Food Chain Model ◽  
Northwestern Mediterranean

Abstract. It is widely recognized that organic carbon exported to the ocean aphotic layer is significantly consumed by heterotrophic organisms such as bacteria and zooplankton in the mesopelagic layer. However, very little is known for the trophic link between bacteria and zooplankton or the function of the microbial loop in this layer. In the northwestern Mediterranean, recent studies have shown that viruses, bacteria, heterotrophic nanoflagellates, and ciliates distribute down to 2000 m with group-specific depth-dependent decreases, and that bacterial production decreases with depth down to 1000 m. Here we show that such data can be analyzed using a simple steady-state food chain model to quantify the carbon flow from bacteria to zooplankton over the mesopelagic layer. The model indicates that bacterial mortality by viruses is similar to or 1.5 times greater than that by heterotrophic nanoflagellates, and that heterotrophic nanoflagellates transfer little of bacterial production to higher trophic levels.

scholarly journals Benthic and Pelagic Viral Decay Experiments: a Model-Based Analysis and Its Applicability

2004 ◽  
Vol 70 (11) ◽  
pp. 6706-6713 ◽  
Author(s):  
Ulrike R. Fischer ◽  
Willy Weisz ◽  
Claudia Wieltschnig ◽  
Alexander K. T. Kirschner ◽  
Branko Velimirov
Keyword(s):  
Mathematical Model ◽  
Curve Fitting ◽  
Bacterial Production ◽  
Time Course ◽  
Decay Rates ◽  
Viral Production ◽  
Viral Control ◽  
Viral Abundance ◽  
Model Based ◽  
Viral Particles

ABSTRACT The viral decay in sediments, that is, the decrease in benthic viral concentration over time, was recorded after inhibiting the production of new viruses. Assuming that the viral abundance in an aquatic system remains constant and that viruses from lysed bacterial cells replace viruses lost by decay, the decay of viral particles can be used as a measure of viral production. Decay experiments showed that this approach is a useful tool to assess benthic viral production. However, the time course pattern of the decay experiments makes their interpretation difficult, regardless of whether viral decay is determined in the water column or in sediments. Different curve-fitting approaches (logarithmic function, power function, and linear regression) to describe the time course of decay experiments found in the literature are used in the present study and compared to a proposed “exponential decay” model based on the assumption that at any moment the decay is proportional to the amount of viruses present. Thus, an equation of the form dVA/dt = −k � VA leading to the time-integrated form VA t = VA0 � e−k � t was used, where k represents the viral decay rate (h−1), VA t is the viral abundance (viral particles ml−1) at time t (h), and VA0 is the initial viral abundance (viral particles ml−1). This approach represents the best solution for an accurate curve fitting based on a mathematical model for a realistic description of viral decay occurring in aquatic systems. Decay rates ranged from 0.0282 to 0.0696 h−1 (mean, 0.0464 h−1). Additionally, a mathematical model is presented that enables the quantification of the viral control of bacterial production. The viral impact on bacteria based on decay rates calculated from the different mathematical approaches varied widely within one and the same decay experiment. A comparison of the viral control of bacterial production in different aquatic environments is, therefore, improper when different mathematical formulas are used to interpret viral decay experiments.

scholarly journals Determinants of mRNA stability in Dictyostelium discoideum amoebae: differences in poly(A) tail length, ribosome loading, and mRNA size cannot account for the heterogeneity of mRNA decay rates.

1988 ◽  
Vol 8 (5) ◽  
pp. 1957-1969 ◽  
Author(s):  
R A Shapiro ◽  
D Herrick ◽  
R E Manrow ◽  
D Blinder ◽  
A Jacobson
Keyword(s):  
Steady State ◽  
Dictyostelium Discoideum ◽  
Mrna Decay ◽  
Decay Rates ◽  
Time Dependent ◽  
Translational Efficiency ◽  
Cdna Clones ◽  
Dependent Manner ◽  
Significant Difference ◽  
Kinetics Of

As an approach to understanding the structures and mechanisms which determine mRNA decay rates, we have cloned and begun to characterize cDNAs which encode mRNAs representative of the stability extremes in the poly(A)+ RNA population of Dictyostelium discoideum amoebae. The cDNA clones were identified in a screening procedure which was based on the occurrence of poly(A) shortening during mRNA aging. mRNA half-lives were determined by hybridization of poly(A)+ RNA, isolated from cells labeled in a 32PO4 pulse-chase, to dots of excess cloned DNA. Individual mRNAs decayed with unique first-order decay rates ranging from 0.9 to 9.6 h, indicating that the complex decay kinetics of total poly(A)+ RNA in D. discoideum amoebae reflect the sum of the decay rates of individual mRNAs. Using specific probes derived from these cDNA clones, we have compared the sizes, extents of ribosome loading, and poly(A) tail lengths of stable, moderately stable, and unstable mRNAs. We found (i) no correlation between mRNA size and decay rate; (ii) no significant difference in the number of ribosomes per unit length of stable versus unstable mRNAs, and (iii) a general inverse relationship between mRNA decay rates and poly(A) tail lengths. Collectively, these observations indicate that mRNA decay in D. discoideum amoebae cannot be explained in terms of random nucleolytic events. The possibility that specific 3'-structural determinants can confer mRNA instability is suggested by a comparison of the labeling and turnover kinetics of different actin mRNAs. A correlation was observed between the steady-state percentage of a given mRNA found in polysomes and its degree of instability; i.e., unstable mRNAs were more efficiently recruited into polysomes than stable mRNAs. Since stable mRNAs are, on average, "older" than unstable mRNAs, this correlation may reflect a translational role for mRNA modifications that change in a time-dependent manner. Our previous studies have demonstrated both a time-dependent shortening and a possible translational role for the 3' poly(A) tracts of mRNA. We suggest, therefore, that the observed differences in the translational efficiency of stable and unstable mRNAs may, in part, be attributable to differences in steady-state poly(A) tail lengths.

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