Abundance Of Virus-like Particles Research Articles

Viral distribution and activity in Antarctic waters

Abstract Variability in abundance of virus-like particles (VLP), VLP decay rates and prokaryotic mortality due to viral infection were determined in three Antarctic areas: Bellingshausen Sea, Bransfield Strait and Gerlache Strait, during December 1995 and February 1996. VLP abundance showed very small spatial variability in the three areas (7×106–2×107 VLP ml−1). VLP abundance, on the other hand, decreased one order of magnitude from the surface to the bottom, in two stations where deep vertical profiles were sampled. Low seasonal variability in VLP abundance was found when comparing each area separately. Diel VLP variability was also very low. VLP abundance showed the lowest values when solar irradiation was maximal, in two of the three stations where diel cycles were examined. Viral decay rates (VDR) were determined using KCN in two kinds of experiments. Type 1 experiments were performed in 6 stations to determine viral decay. Type 2 experiments were carried out in 2 stations to examine the influence of temperature and organic matter concentration on viral decay. VDR was not influenced by these parameters. Prokaryotic mortality due to viral infection was always higher than that due to bacterivores in the stations where both factors of prokaryotic mortality were measured. Viral infection accounted for all the prokaryotic heterotrophic production in Bellingshausen Sea and Gerlache Strait and for half of the prokaryotic heterotrophic production in Bransfield Strait. These high values of prokaryotic mortality due to viral infection are difficult to reconcile in nature, and more work is necessary to determine the mechanisms involved in the disappearance of viruses.

Viruses in the plankton of freshwater and saline Antarctic lakes

1. Virus‐like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68° S) were determined in December 1999. In the ultra‐oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 × 106 mL–1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 × 106 mL–1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter.2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star‐like particles of about 80 nm diameter.3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers or chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r=0.845, P < 0.01).4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus‐like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy.5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems.

Seasonal dynamics of viruses in an alpine lake: importance of filamentous forms

Viruses are an important component of the planktonic food web in freshwater and marine systems, but most studies have been done in the ocean and in lowland lakes. In this work, the seasonal dynamics and structure of the virioplankton as well as their impact on bacteria during a day/night cycle were studied in an alpine lake located 2417 m above sea level. The abundance of virus-like particles (VLP) was determined at 5 discrete depths (0.5 to 8 m) by direct counts with a TEM in samples collected from May to November 1998 at weekly to bi-weekly intervals. Viruses reached the highest abundances under ice (4.6 × 106 VLP ml–1) with a second maximum in autumn. After ice-break, the VLP abundance decreased to undetectable values ( 10 μm) and their respective abundances were positively correlated (rs = 0.728, p < 0.01). The absence of these conspicuous forms in other aquatic ecosystems suggests that FVLP are well adapted to the harsh environmental conditions or are specific to bacterial hosts found in alpine lakes. Finally, between 5 and 28% of the newly produced bacteria were killed by non-filamentous viruses, which therefore are a modest cause of bacterial mortality in this lake.

Bacterial carbon production in Lake Erie is influenced by viruses and solar radiation

Bacterial production is an integral recycling mechanism that facilitates carbon flow through aquatic food webs. Factors influencing bacterial activity therefore impact carbon flow. Although ecologists consider grazing and dissolved organic carbon flux to be the major regulators of bacterial activity, we explored two other important pressures. Virus-like particle abundance ranged from 3.7 × 1010to 37.9 × 1010·L-1in samples collected during August 1997 and July 1998. Bacterial abundance during these periods ranged from 1.8 × 109to 4.6 × 109·L-1. Based on electron microscopic analysis, viruses in Lake Erie would have been responsible for 12.1-23.4% of bacterial mortality and, in quasi-steady-state conditions, a comparable loss of bacterial productivity. In the central basin, solar radiation was also demonstrated to regulate bacterial productivity. Ultraviolet radiation (295-400 nm) was shown to inhibit bacterial productivity according to a cumulative exposure kinetic model, and biological weighting functions were derived to enable calculation of time- and depth-integrated photoinhibition. The daytime photoinhibitory loss of bacterial carbon production was estimated to be 14-30% over the upper 5 m, primarily due to ultraviolet radiation &gt;320 nm. Viruses and sunlight are therefore of comparable importance as regulators of bacterial activity in this system.

An in situ enclosure experiment to test the solar UVB impact on plankton in a high-altitude mountain lake. II. Effects on the microbial food web

We studied the impact of ambient levels of solar ultraviolet B (UVB) radiation on the planktonic microbial food web (viruses, heterotrophic bacteria, heterotrophic nanoflagellates and ciliates) of a high-mountain lake (2417 m above sea level) under <it>in situ</it> conditions for 16 days. Enclosures of 1 m³ receiving either the full sunlight spectrum or sunlight without UVB radiation were suspended at the lake surface. We found that the abundance of heterotrophic nanoflagellates was always lower in the +UVB treatment than in the -UVB one. In addition, bacterial consumption, measured by the disappearance of fluorescently labelled bacteria, was significantly (P &lt; 0.05) reduced in the +UVB treatment. The abundance of non-filamentous bacteria (&lt;10 <IMG SRC="/math/mu.gif">m long) was also lower in the +UVB treatment, suggesting a direct effect of UVB on their growth. This was supported by the significantly (P &lt; 0.05) lower cell-specific activity ([³H])thymidine incorporation) found on the fifth day of the experiment. In contrast, UVB radiation had no effect on filamentous bacteria (&gt;1 &mgr;m long), which represented only a small fraction of the total abundance (&lt;4%), but up to 70% of the total bacterial biovolume. Ciliates, mainly <it>Urotricha pelagica</it> and <it>Urotricha furcata</it>, were less impacted by UVB radiation, although the net growth rate during the first week of the experiment was lower in the +UVB treatment than in the -UVB one (0.22 and 0.39 day^-1, respectively). The abundance of virus-like particles during the first week of the experiment was higher in the -UVB treatment. After reaching the maximum value for the interaction viruses x bacteria, viral abundance decreased dramatically (by 85%) in both treatments with a decay rate of 0.017 h^-1. This study illustrates the complexity in assessing the impact of UVB radiation when more than one trophic level is considered and indicates the existence of different sensitivity to UVB radiation among components of the microbial food web.

Distribution of viruses and their potential effect on bacterioplankton in an oligotrophic marine system

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 19:205-213 (1999) - doi:10.3354/ame019205 Distribution of viruses and their potential effect on bacterioplankton in an oligotrophic marine system Núria Guixa-Boixereu, Dolors Vaqué, Josep M. Gasol, Carlos Pedrós-Alió* Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar, CSIC, Passeig Joan de Borbó s/n, 08038 Barcelona, Spain *Addressee for correspondence. E-mail: cpedros@icm.csic.es ABSTRACT: Diel and spatial variability in the concentration of virus-like particles (VLP) was determined in a transect from the coast to offshore in the western Mediterranean (7 stations and 6 depths per station). VLP abundance in coastal waters was on average 1.6 x 107 VLP ml-1, in offshore stations this value was 1.2 x 107 VLP ml-1. At the coastal station there was no varaibility in VLP abundance, bacterial abundance or chlorophyll a concentration through the water column, while offshore VLP decreased with depth. No clear diel pattern was found in 3 representative stations where diel cycles were studied. Viral impact on the bacterial assemblage was estimated at 2 depths (surface and deep chlorophyll a maximum) of the latter 3 stations using 2 approaches: the percentage of visibly infected bacteria and viral decay rates in cyanide amended cultures. Visibly infected bacteria could not be detected in any sample after counting 300 cells per sample, implying that the percentage of visibly infected bacteria was lower than 0.3%. Using the maximal conversion factor to convert this value to bacterial mortality we found that viruses could be responsible at most for 21.5% of the whole bacterial mortality. We calculated a hypothetical viral decay rate if the maximal possible impact of viruses (21.5%) were true. This value corresponded to 0.02 h-1. However, using the cyanide method to measure viral decay rate, no significant decrease could be detected in a total of 8 viral decay experiments. In conclusion, the percent of total bacterial mortality due to viral lysis in the oligotrophic northwestern Mediterranean was low, certainly much lower than 20%. KEY WORDS: Oligotrophy · Mediterranean Sea · Virus-like particles (VLP) · Diel cycles · Viral decay · Viral impact Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 19, No. 3. Publication date: October 27, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Abundance of viruses in deep oceanic waters

Vertical distributions of bactena and viruses were Investigated in the oceanic stations located in subarctic (Stn A) and subtropical (Stn B) areas of the Paciflc using the direct count technique and transmission electron microscopy. Small DAPI-positive, virus-like particles (VLP) were found to be distributed throughout the water column down to 5000 m a t both of the stations. The abundance of VLP ranged from 38 X 10' ml-' a t 50 m depth to 0.6 X 10' ml-' at 5000 m depth a t Stn A. The ratio of VLP to bacteria-like particle (BLP) ranged from 1.1 to 7.4 a t Stn A and 1.0 to 8.7 at Stn B in the entire water column. The maximum ratio was recorded at Stn B from the deepest sample, collected at a depth of 5000 m. The electron microscopic investigation Indicated that the major proportion of VLP were probably viruses.

Seasonal variations of virus abundance and viral control of the bacterial production in a backwater system of the danube river

The abundance of virus-like particles in a backwater system of the Danube River covered a range of 1.2 x 10(sup7) to 6.1 x 10(sup7) ml(sup-1) from 1992 to 1993. Measurements of head diameters for these particles, all of which were presumed to be viruses, led to four defined size classes, ranging from <60 nm to >150 nm. The 60- to <90-nm size class contained the largest fraction of total particles (41%), followed by the 90- to <150-nm size class (33%). The frequency of size classes was not significantly different between the two years. The frequency of bacteria with mature phages ranged from 1 to 4% over the seasons, with mean burst sizes ranging from 17 to 36 phage per host cell. Among the bacterial morphotypes, rods and vibrios were the major host systems for phages, while coccoid and filamentous cells were considered negligible. Counts from transmission electron microscopy and acridine orange direct counts confirmed that rods and vibrios accounted for 85 to 95% of the bacterial population over the seasons. Virus decay experiments showed lower decay rates for temperatures between 5 and 15(deg)C (52 to 70% of the virus population remained) relative to 18 and 25(deg)C (31 to 51% of the virus remained). Bacterial production measurements, performed at the same time and under the same conditions as decay experiments, allowed us to estimate virus-induced death rates, which ranged from 15.8 to 30.1% over the year, with an average of 20% viral control of the bacterial production. Considering that mature phage particles are visible only in the last phase of the latent period and using a mean conversion factor of 5.4 from the literature, based on descriptions of various phage host systems to relate the percentage of visibly infected cells to the total percentage of the bacterial community that is phage infected, we estimate that some 5.4 to 21.6% of the bacterial population is infected with viruses. This would imply that virus-induced death rates of bacteria range from 10.8 to 43.2%. The data on virus-induced bacterial mortality obtained by both the viral decay method and the determination of the frequency of infected cells are compared and discussed.

Effects of colloidal organic matter on the growth of bacteria and protists in lake water

The impact of colloids of subbacterial size on the growth of bacteria and heterotrophic flagellates in lake water was studied. Colloidal organic matter <0.2 µm but >100 kD was concentrated from the water of four lakes, and growth of microorganisms was compared in water with and without added colloid concentrate. A tenfold increase in the concentration of colloids had either no effect on bacteria or supported an increase in bacterial yield of ≤80% in predator-free samples. Growth of flagellates was also stimulated by the enhanced colloid concentration. In two of the lakes, increased colloid concentration resulted in more flagellates produced per unit of bacteria consumed, indicating that colloids served as a supplementary source of nutrition. However, enhancement of the colloid concentration did not influence flagellate-bacterial predator-prey patterns, suggesting that bacteria were still the major food source of flagellates despite increased abundance of colloids of subbacterial size. In addition, in experiments with water from a eutrophic lake, abundance of viruslike particles (VLP) was monitored. At natural colloid concentration as well as at tenfold enhanced colloid concentration, abundance of VLP decreased in samples containing heterotrophic flagellates, but did not decrease in samples without flagellates. Assuming the decrease in VLP was due to ingestion by flagellates, the calculated contribution of VLP carbon to the total carbon demand of flagellates was only marginal (0.09–0.2%).

Characterization of virus-like particles produced by a recombinant baculovirus containing the gag gene of the bovine immunodeficiency-like virus

The entire gag gene of the bovine immunodeficiency-like virus (BIV) was inserted behind the strong polyhedron promoter of Autographa californica nuclear polyhedrosis virus (AcNPV). The resultant recombinant baculovirus (AcNPV-BIV gag ) was used to infect insect cells in order to overexpress and characterize BIV gag gene products. The infection resulted in the high-level expression of a protein similar in size to the predicted BIV gag precursor (Pr53 gag ). BIV Pr53 gag was detected in AcNPV-BIV gag -infected insect cells and in culture supernatants. Electron microscopy of these cells revealed an abundance of virus-like particles (VLPs) in the cytoplasm, budding from the cell membrane, and free in the culture medium. The size and morphology of the VLPs were similar to those of the immature forms of BIV observed in infected mammalian cells. The VLPs sedimented at a density of 1.16 g of sucrose per milliliter in linear gradients and were shown to contain the majority of the supernatant Pr53 gag . Antigenic determinants on Pr53 gag from VLPs were recognized by BIV and HIV-1 antiserum, and serum from rats immunized with VLPs reacted with recombinant and viral BIV Pr53 gag and processed products. The protease (PR) activity in BIV virions was capable of processing recombinant Pr53 gag ; this activity was blocked by pepstatin A, a potent aspartyl PR inhibitor. Baculovirus-expressed BIV Pr53 gag appears to be an excellent source of gag precursor; it may prove useful for structural studies and enable the development of assays to detect retroviral PR inhibitors. The data further suggest that unprocessed BIV Pr53 gag plays a major role in the assembly of BIV particles. The expression of other BIV structural genes in insect cells may prove instructive in the study of molecular events involved in the assembly and processing of these BIV proteins.

Ultrastructure of the compound eye of the diploid female beetle, Xyleborus ferrugineus.

The compound eye of female (diploid) Xyleborus ferrugineus beetles was examined with scanning and transmission electron microscopy. The eye is emarginate, and externally consists of roughly 70-100 facets. Each ommatidium is composed of a thickly biconvex lenslet with about 50 electron dense and rare layers. The lens facet overlies a crystalline cone of the acone type which is roughly hourglass-shaped. Pigment cells envelop the entire ommatidium, and pigment granules also are abundant throughout the cytoplasm of the 8 retinular cells. The rhabdomeres of 2 centrally situated photoreceptor cells effectively fuse into a rhabdom that extends from the base of the crystalline cone deeply into the ommatidium. Six distal peripheral retinular cells encircle the 2 central cells, and their rhabdomeres join laterally to form a rhabdomeric ring around the central rhabdom. The rhabdom and rhabdomeric ring are effectively separated by the cytoplasm of the two central retinular cells which contains the usual organelles and an abundance of shielding pigment granules. Eight axons per ommatidium gather in a tracheae-less fascicle before exiting the eye through the fenestrate basement membrane. No tracheation was observed among the retinular cells. Each Semper cell of each observed crystalline cone contained an abundance of virus-like particles near the cell nucleus. The insect is laboratory reared, and the visual system seems very amenable to photoreceptor investigations.