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Though microbial processes in the oxygen minimum zones (OMZs) of the Arabian Sea (AS) are well documented, prokaryote-virus interactions are less known. The present study was carried out to determine the potential physico-chemical factors influencing viral abundances and their life strategies (lytic and lysogenic) along the vertical gradient in the OMZ of the AS (southwest coast of India). Water samples were collected during the southwest monsoon (SWM) season in two consecutive years (2015 and 2016) from different depths, namely, the surface layer, secondary chlorophyll a maxima (~30⁻40 m), oxycline (~70⁻80 m), and hypoxic/suboxic layers (~200⁻350 m). The high viral abundances observed in oxygenated surface waters (mean ± SD = 6.1 ± 3.4 × 106 viral-like particles (VLPs) mL−1), drastically decreased with depth in the oxycline region (1.2 ± 0.5 × 106 VLPs mL−1) and hypoxic/suboxic waters (0.3 ± 0.3 × 106 VLPs mL−1). Virus to prokaryote ratio fluctuated in the mixed layer (~10) and declined significantly (p < 0.001) to 1 in the hypoxic layer. Viral production (VP) and frequency of virus infected cells (FIC) were maximum in the surface and minimum in the oxycline layer, whereas the viral lysis was undetectable in the suboxic/hypoxic layer. The detection of a high percentage of lysogeny in suboxic (48%) and oxycline zones (9⁻24%), accompanied by undetectable rates of lytic viral infection support the hypothesis that lysogeny may represent the major survival strategy for viruses in unproductive or harsh nutrient/host conditions in deoxygenated waters.

Viruses profoundly influence benthic marine ecosystems by infecting and subsequently killing their prokaryotic hosts, thereby impacting the cycling of carbon and nutrients. Previously conducted studies, based on different methodologies, have provided widely differing estimates of the relevance of viruses on benthic prokaryotes. There has been no attempt so far to compare these independent approaches, including contextual comparisons among different approaches for sample manipulation (i.e., dilution or not of the sediments during incubations), between methods based on epifluorescence microscopy (EFM) or radiotracers, and between the use of different radiotracers. Therefore, it has been difficult to identify the most suitable methodologies and protocols to be used as standard approaches for the quantification of viral infections of prokaryotes. Here, we compared for the first time different methods for determining viral and prokaryotic production rates in marine sediments collected at two benthic sites, differing in depth and environmental conditions. We used a highly replicated experimental design, testing the potential biases associated to the incubation of sediments as diluted or undiluted. In parallel, we also compared EFM counts with the ³H-thymidine incubations for the determination of viral production rates, and the use of ³H-thymidine versus ³H-leucine radiotracers for the determination of prokaryotic production. We show here that, independent from sediment dilution, EFM-based values of viral production ranged from 1.4 to 4.6 x 107 viruses g-1 h-1, and were similar but overall less variable compared to those obtained by the ³H-thymidine method (0.3 to 9.0 x 107 viruses g-1 using the ³H-thymidine or ³H-leucine method, respectively). These results indicated that viral lysis was responsible for the abatement of 55-81% of the prokaryotic heterotrophic production, corroborating previous findings of the major role of viruses in benthic deep-sea ecosystems. Moreover, our methodological comparison for the analysis of viral production in marine sediments suggests that microscopy-based approaches are simpler and more cost-effective than those based on radiotracers. These approaches also reduce time to results and overcome issues related to generation of radioactive waste. [ABSTRACT FROM AUTHOR]h-1). In addition, the prokaryotic production rates were not affected by sediment dilution, and the use of different radiotracers provided very consistent estimates (10.3-35.1 and 9.3-34.6 ngC g-1 h-1 using the ³H-thymidine or ³H-leucine method, respectively). These results indicated that viral lysis was responsible for the abatement of 55-81% of the prokaryotic heterotrophic production, corroborating previous findings of the major role of viruses in benthic deep-sea ecosystems. Moreover, our methodological comparison for the analysis of viral production in marine sediments suggests that microscopy-based approaches are simpler and more cost-effective than those based on radiotracers. These approaches also reduce time to results and overcome issues related to generation of radioactive waste. [ABSTRACT FROM AUTHOR]

The viral and bacterioplankton communities of the Barents Sea were investigated using a combination of methods of electron and epifluorescence microscopy for the first time. The quantitative composition of the communities and the nature of their interactions were also determined. Our study showed that during the summer the abundance and biomass of bacterioplankton reached 0.4-4.0 × 10 cells/mL and 25.09-84.21 mg/m in offshore waters and 0.4-1.8 × 10 cells/mL and 19.63-100.19 mg/m in coastal waters, respectively. In both regions, the number of viruses (1.7-35.8 × 10 and 14.5-32.4 × 10 particles/mL) exceeded the number of bacteria by 2-31 and 13-60 times, respectively; the average viral production was 0.7510 and 1.74 × 10 particles/mL/day, respectively. The proportion of infected cells in the total bacterioplankton (7% on average) and virus-induced mortality of bacteria (8%) were much lower in offshore than in coastal waters (14 and 20%, respectively). [ABSTRACT FROM AUTHOR]

Understanding the mechanism of HIV-1 latency is crucial to the viral reservoir eradication. Human cellular miRNAs can modulate HIV-1 expression by targeting of viral RNAs or host gene transcripts. To identify miRNAs modulating HIV-1 latency, we determined the miRNA expression profiles of HIV-1 latently infected and productively infected cells by microarray and qRT-PCR. Among the differentially expressed miRNAs, miR-196b and miR-1290 targeted the 3′ untranslated region of HIV-1 and affected its expression. Ectopic expression of these two miRNAs efficiently suppressed HIV-1 production and infectivity. Specific inhibitors of these miRNAs substantially counteracted their effects on HIV-1, as measured either as viral production and infectivity in HEK-293T cells or as HIV-1 RNA expression or viral production in cells isolated from HIV-1-infected individuals. Our study emphasizes the role of cellular miRNAs in HIV-1 latency regulation, and it suggests that inhibitors of miR-196b and miR-1290 could be used to activate latent HIV-1. [ABSTRACT FROM AUTHOR]

Siglecs, sialic acid-recognizing Ig-superfamily lectins, regulate various aspects of immune responses, and have also been shown to induce the endocytosis of binding materials such as anti-Siglec antibodies or sialic acid-harboring bacteria. In this study, we demonstrated that the expression of Siglec-9 enhanced the transfection efficiency of several cell lines such as macrophage RAW264 and non-hematopoietic 293FT cells. We applied this finding to the production of a lentiviral vector in which cells were transfected simultaneously with multiple vectors, and achieved a twice increase in viral production levels. Furthermore, 293FT cells expressing lectin-defective Siglec-9 produced three- to seven-fold higher titer of viral vector compared with parental 293FT cells. These results suggest that Siglec-9 enhanced lentiviral vector production in a lectin-independent manner. [ABSTRACT FROM AUTHOR]

Numerous viruses manipulate host factors for viral production. We demonstrated that human enterovirus A71 (EVA71), a primary causative agent for hand, foot, and mouth disease (HFMD), increased the level of the DNA damage response (DDR) marker γ-H2AX. DDR is primarily mediated by the ataxia telangiectasia mutated (ATM), ATM and Rad3-related (ATR), or DNA-dependent protein kinase (DNA-PK) pathways. Upregulation of γ-H2AX by EVA71 was dependent on the ATR but not the ATM or DNA-PK pathway. As a nuclear factor, there is no previous evidence of cytoplasmic distribution of γ-H2AX. However, the present findings demonstrated that EVA71 encouraged the localization of γ-H2AX to the cytoplasm. Of note, γ-H2AX formed a complex with structural protein VP3, non-structural protein 3D, and the viral genome. Treatment with an inhibitor or CRISPR/Cas9 technology to decrease or silence the expression of γ-H2AX decreased viral genome replication in host cells; this effect was accompanied by decreased viral protein expression and virions. In animal experiments, caffeine was used to inhibit DDR; the results revealed that caffeine protected neonatal mice from death after infection with EVA71, laying the foundation for new therapeutic applications of caffeine. More importantly, in children with HFMD, γ-H2AX was upregulated in peripheral blood lymphocytes. The consistent in vitro and in vivo data on γ-H2AX from this study suggested that caffeine or other inhibitors of DDR might be novel therapeutic agents for HFMD.

Microbes play a central role in the decomposition and remineralization of organic matter and recycling of nutrients in aquatic environments. In this study, we examined the influence of physical, chemical, and biological parameters on the rate of bacterial production (BP) and viral production (VP) with respect to primary production over a diurnal period in Cochin estuary. Time series measurements were made every 2 h for 12 h (6 a.m.-6 p.m.) during periods of low and high salinities. The light intensity as photosynthetically active radiation, temperature, salinity, nutrients like NO-N, SiO-Si, and PO-P, and chlorophyll a (Chl a) were measured along with BP, VP, and net primary production (NPP). NPP showed a strong positive correlation with light and Chl a ( r = 0.56 and 0.47, respectively), while VP showed a strong positive correlation with light, salinity, and Chl a ( r = 0.37, 0.58, and 0.37, respectively) and a negative correlation with BP ( r = −0.39) at P ≤ 0.05. We observed a diurnal pattern in BP but did not have any significant correlation with light. Similar diurnal pattern was seen in VP, the peak of which was in succession with BP, suggesting that virus-mediated lysis plays an important role in loss processes of bacteria in Cochin estuary. The results of our study highlight the light-dependent and physicochemical-dependent diurnal variation in virioplankton production in a tropical estuarine ecosystem. [ABSTRACT FROM AUTHOR]

Abstract: Rotavirus (RV) infection causes serious dehydrating diarrhoea in infants and newborn animals. Our previous study revealed that cyclophilin A (CYPA), a peptidyl-prolyl cis–trans isomerase (PPIase), could be temporarily upregulated in RV-infected MA104 cells in early stage of infection (unpublished data). To find out the possible roles of CYPA in RV infection, we overexpressed and silenced CYPA in various cell lines by gene transfection and shRNA. We found that transfection of CYPA significantly inhibited RV replication, while silencing the expression of CYPA significantly increased RV replication. Accordingly, overexpression of CYPA significantly increased IFN-β production; while silencing CYPA significantly reduced IFN-β production. This effect of CYPA on IFN-β production was independent of its PPIase activity. Moreover, IFN-β secreted by host cells in RV infection had a critical repressive effect on viral replication. Finally, we found that inhibiting JNK pathway by SP600125 and JNK siRNA abrogated the effect of CYPA on IFN-β transcription in RV-infected MA104 cells. Together, our data suggested that CYPA inhibited RV replication by facilitating host IFN-β production, which was independent on the PPIase activity of CYPA but dependent on the activation of JNK signaling pathway. [Copyright &y& Elsevier]

Background: Over the last 30 years, extensive studies have revealed the crucial roles played by microbes in aquatic ecosystems. It has been shown that bacteria, viruses and protozoan grazers are dominant in terms of abundance and biomass. The frequent interactions between these microbiological compartments are responsible for strong trophic links from dissolved organic matter to higher trophic levels, via heterotrophic bacteria, which form the basis for the important biogeochemical roles of microbial food webs in aquatic ecosystems. To gain a better understanding of the interactions between bacteria, viruses and flagellates in lacustrine ecosystems, we investigated the effect of protistan bacterivory on bacterial abundance, production and structure [determined by 16S rRNA PCR-DGGE], and viral abundance and activity of two lakes of contrasting trophic status. Four experiments were conducted in the oligotrophic Lake Annecy and the mesotrophic Lake Bourget over two seasons (early spring vs. summer) using a fractionation approach. In situ dark vs. light incubations were performed to consider the effects of the different treatments in the presence and absence of phototrophic activity. Results: The presence of grazers (i.e. < 5-μm small eukaryotes) affected viral production positively in all experiments, and the stimulation of viral production (compared to the treatment with no eukaryotic predators) was more variable between lakes than between seasons, with the highest value having been recorded in the mesotrophic lake (+30%). Viral lysis and grazing activities acted additively to sustain high bacterial production in all experiments. Nevertheless, the stimulation of bacterial production was more variable between seasons than between lakes, with the highest values obtained in summer (+33.5% and +37.5% in Lakes Bourget and Annecy, respectively). The presence of both predators (nanoflagellates and viruses) did not seem to have a clear influence upon bacterial community structure according to the four experiments. Conclusions: Our results highlight the importance of a synergistic effect, i.e. the positive influence of grazers on viral activities in sustaining (directly and indirectly) bacterial production and affecting composition, in both oligotrophic and mesotrophic lakes. [ABSTRACT FROM AUTHOR]

Here, for the first time, we have carried out synoptic measurements of viral production and decay rates in continental-shelf and deep-sea sediments of the Mediterranean Sea to explore the viral balance. The net viral production and decay rates (1.1–61.2 and 0.6–13.5 × 107 viruses g−1 h−1, respectively) were significantly correlated, and were also related to prokaryotic heterotrophic production. The addition of enzymes increased the decay rates in the surface sediments, but not in the subsurface sediments. Both the viral production and the decay rates decreased significantly in the deeper sediment layers, while the virus-to-prokaryote abundance ratio increased, suggesting a high preservation of viruses in the subsurface sediments. Viral decay did not balance viral production at any of the sites investigated, accounting on average for c. 32% of the gross viral production in the marine sediments. We estimate that the carbon (C) released by viral decay contributed 6–23% to the total C released by the viral shunt. Because only c. 2% of the viruses produced can infect other prokaryotes, the majority is not subjected to direct lysis and potentially remains as a food source for benthic consumers. The results reported here suggest that viral decay can play an important role in biogeochemical cycles and benthic trophodynamics. [ABSTRACT FROM AUTHOR]

Efficient inhibition of the HIV infection life cycle at the stages of viral infection, reverse transcription, and post-translational processing has been extensively studied. However, efficient inhibition of HIV assembly and budding has not been reported. Here, we report that dendritic cell-specific intercellular adhesion molecule-3 (ICAM-3) -grabbing nonintegrin (DC-SIGN) and its related protein, DC-SIGNR, effectively block HIV budding from infected cells. Cotransfection of DC-SIGN or DC-SIGNR with HIV demonstrated 95-99.5% inhibition of viral production from host cells. DC-SIGN or DC-SIGNR can also effectively inhibit 90-95% of HIV generation from infected cells. DC-SIGN efficiently reduces the amount of gp120 present on the cell plasma membrane, and completely strips off gp120 from the virions produced by the host cells, suggesting that blockage of HIV budding is due to internalization of gp120 by DC-SIGN. [ABSTRACT FROM AUTHOR]

Abstract: The production of hemagglutinating virus of Japan (HVJ; Sendai virus) was inhibited at 41°C, whereas it was normal at 37°C. In the infected Vero cells, viral specific proteins were synthesized even at 41°C, but the synthesized HN protein was not integrated into the cell membrane, resulting in the inhibition of viral production. To investigate the relationship of HSP70 to the inhibition of HN-protein integration, the expression of HSP70 was induced by prostaglandin A1 (PGA1) at 37°C, and the influence on viral infection was examined. The induction of HSP70 at 37°C inhibited the viral production. Viral proteins were also synthesized, even in the presence of PGA1. However, HN protein was not as present on the cell membrane following PGA1-treatment as it was at 41°C, whereas F protein was detected. An immunoprecipitation assay showed that HSP70 was coprecipitated with HN protein, but not with F protein. The results suggested that the specific interaction of HSP70 with HN protein prevented the protein from integrating into the cell membrane. In addition, the abnormal virus-like particles, of which HN protein and nucleocapsid were ablated, were released in the culture medium at 41°C, although the size was smaller than the normal viral virions. The results suggest that HN protein is necessary for viral morphogenesis. [Copyright &y& Elsevier]

The cellular prion protein (PrPc) is highly conserved in mammals and expressed widely in different tissues but its physiological role remains elusive. Recently, the human PrPc was shown to possess nucleic acid binding and chaperoning properties similar to human immunodeficiency virus type 1 (HIV-1) nucleocapsid protein, a key viral factor in virus structure and replication. These findings prompted us to determine if PrPc could influence HIV-1 replication. We used the human 293T cell line as a model system, since only a very low level of PrPc accumulates in these cells. Expression of PrP at a high level resulted in a specific decrease of HIV-1 Env and Vpr expression. Despite similar levels of intracellular Gag, virus production was reduced by eightfold and infectivity by three- to fourfold in the presence of PrPc. A PrPc mutant lacking the glycosylphosphatidylinositol (GPI) anchor peptide did not impair HIV-1 production, suggesting that PrPc trafficking is critical for this inhibitory effect. Coexpressing HIV-1 and PrPc in these cells also caused a fraction of PrPc to become partially proteinase K-resistant (PrPres), further illustrating the interactions between HIV-1 and PrPc. [Copyright &y& Elsevier]

To indentify a plausible large-scale production system forretroviral vector, three culture systems, i.e., batch culturewith medium exchange, microcarrier culture, and packed-bedreactor culture were compared. In batch cultures with mediumexchange, high cell concentrations were maintained for about amonth, and the harvested retroviral titer remained constant. Inmicrocarrier cultures, although cell growth was rapid, theretroviral titer was unexpectedly low, suggesting that the lowtiter was due either to serious damage to the retroviral vectoror to a reduction in the production rate of retroviral vector,caused by mechanical shear forces. Although the retroviral titer(maximum titer, 1.56 × 106) in the packed-bedreactor was a little bit lower than that obtained in the batchculture with medium exchange (maximum titer, 1.91 ×106), continuous production made it possible to increasethe cumulative titer up to 16-fold of that from the batchculture with medium exchange. Moreover, as the packed-bedreactor system requires less labor and shows excellentvolumetric productivity in comparison to batch cultures withmedium exchanges, it will be an appropriate production systemfor retroviral vector in large quantities. [ABSTRACT FROM AUTHOR]

• We present a novel ODE model of RSV that includes the effect of syncytia. • Effect of syncytia occurs when R0 from syncytia equals R0 from cell-free transmission. • High fusion rate & low viral production in syncytia leads to slow-growing infections. Respiratory syncytial virus (RSV) is a common, contagious infection of the lungs and the respiratory tract. RSV is characterized by syncytia, which are multinuclear cells created by cells that have fused together. We use a mathematical model to study how different assumptions about the viral production and lifespan of syncytia change the resulting infection time course. We find that the effect of syncytia on viral titer is only apparent when the basic reproduction number for infection via syncytia formation is similar to the reproduction number for cell free viral transmission. When syncytia fusion rate is high, we find the presence of syncytia can lead to slowly growing infections if viral production is suppressed in syncytia. Our model provides insight into how the presence of syncytia can affect the time course of a viral infection. [ABSTRACT FROM AUTHOR]

Papillomavirus L1 and L2, the major and minor capsid proteins, play significant roles in viral assembly, entry, and propagation. In the current study, we investigate the impact of L1 and L2 on viral life cycle and tumor growth with a newly established mouse papillomavirus (MmuPV1) infection model. MmuPV1 L1 knockout, L2 knockout, and L1 plus L2 knockout mutant genomes (designated as L1ATGko-4m, L2ATGko, and L1-L2ATGko respectively) were generated. The mutants were examined for their ability to generate lesions in athymic nude mice. Viral activities were examined by qPCR, immunohistochemistry (IHC), in situ hybridization (ISH), and transmission electron microscopy (TEM) analyses. We demonstrated that viral DNA replication and tumor growth occurred at both cutaneous and mucosal sites infected with each of the mutants. Infections involving L1ATGko-4m, L2ATGko, and L1-L2ATGko mutant genomes generally resulted in smaller tumor sizes compared to infection with the wild type. The L1 protein was absent in L1ATGko-4m and L1-L2ATGko mutant-treated tissues, even though viral transcripts and E4 protein expression were robust. Therefore, L1 is not essential for MmuPV1-induced tumor growth, and this finding parallels our previous observations in the rabbit papillomavirus model. Very few viral particles were detected in L2ATGko mutant-infected tissues. Interestingly, the localization of L1 in lesions induced by L2ATGko was primarily cytoplasmic rather than nuclear. The findings support the hypothesis that the L2 gene influences the expression, location, transport, and assembly of the L1 protein in vivo. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Climate warming can directly affect biological processes in marine environments. Here, we investigated if warming (+2 °C) can change dynamics in viral and prokaryotic populations in the cold seasons in natural seawaters. We monitored the changes in viral production and prokaryotic growth rate. The prokaryotic average gross growth rates were 0.08 and 0.34 h−1 in November and 0.06 and 0.41 h−1 in December in the in situ and warming experiments, respectively. We found that warming water temperature resulted in a significant increase in prokaryotic growth rates. In warming experiments, the overall viral production rate was about 0.77–14.4 × 105 viruses mL−1 h−1, and a rough estimate of prokaryotic mortality was about 5.6–6.8 × 104 cells mL−1 h−1. Based on our estimation, burst sizes of about 21 and 14 viruses prokaryotes−1 were measured under the experimental warming period. Moreover, the results found that an increased water temperature in the subtropical western Pacific coastal waters increases prokaryotic growth rates, enhances viral production, and changes the carbon fluxes in the trophic interactions of microbes. [ABSTRACT FROM AUTHOR]

Viruses are the most abundant microorganisms in marine environments and viral infections can be either lytic (virulent) or lysogenic (temperate phage) within the host cell. The aim of this study was to quantify viral dynamics (abundance and infection) in the coastal Red Sea, a narrow oligotrophic basin with high surface water temperatures (22–32 °C degrees), high salinity (37.5–41) and continuous high insolation, thus making it a stable and relatively unexplored environment. We quantified viral and environmental changes in the Red Sea (two years) and the occurrence of lysogenic bacteria (induced by mitomycin C) on the second year. Water temperatures ranged from 24.0 to 32.5 °C, and total viral and bacterial abundances ranged from 1.5 to 8.7 × 106 viruses mL−1 and 1.9 to 3.2 × 105 bacteria mL−1, respectively. On average, 12.24% ± 4.8 (SE) of the prophage bacteria could be induced by mitomycin C, with the highest percentage of 55.8% observed in January 2018 when bacterial abundances were low; whereas no induction was measurable in spring when bacterial abundances were highest. Thus, despite the fact that the Red Sea might be perceived as stable, warm and saline, relatively modest changes in seasonal conditions were associated with large swings in the prevalence of lysogeny. [ABSTRACT FROM AUTHOR]

Abstract Background Over the last 30 years, extensive studies have revealed the crucial roles played by microbes in aquatic ecosystems. It has been shown that bacteria, viruses and protozoan grazers are dominant in terms of abundance and biomass. The frequent interactions between these microbiological compartments are responsible for strong trophic links from dissolved organic matter to higher trophic levels, via heterotrophic bacteria, which form the basis for the important biogeochemical roles of microbial food webs in aquatic ecosystems. To gain a better understanding of the interactions between bacteria, viruses and flagellates in lacustrine ecosystems, we investigated the effect of protistan bacterivory on bacterial abundance, production and structure [determined by 16S rRNA PCR-DGGE], and viral abundance and activity of two lakes of contrasting trophic status. Four experiments were conducted in the oligotrophic Lake Annecy and the mesotrophic Lake Bourget over two seasons (early spring vs. summer) using a fractionation approach. In situ dark vs. light incubations were performed to consider the effects of the different treatments in the presence and absence of phototrophic activity. Results The presence of grazers (i.e. < 5-μm small eukaryotes) affected viral production positively in all experiments, and the stimulation of viral production (compared to the treatment with no eukaryotic predators) was more variable between lakes than between seasons, with the highest value having been recorded in the mesotrophic lake (+30%). Viral lysis and grazing activities acted additively to sustain high bacterial production in all experiments. Nevertheless, the stimulation of bacterial production was more variable between seasons than between lakes, with the highest values obtained in summer (+33.5% and +37.5% in Lakes Bourget and Annecy, respectively). The presence of both predators (nanoflagellates and viruses) did not seem to have a clear influence upon bacterial community structure according to the four experiments. Conclusions Our results highlight the importance of a synergistic effect, i.e. the positive influence of grazers on viral activities in sustaining (directly and indirectly) bacterial production and affecting composition, in both oligotrophic and mesotrophic lakes.

The lytic and lysogenic life cycles of marine phages are influenced by environmental conditions such as solar radiation, temperature, and host abundance. Temperature can regulate phage infection, but its role is difficult to discern in oligotrophic waters where there is typically low host abundance and high temperatures. Here, we study the temporal variability of viral dynamics and the occurrence of lysogeny using mitomycin C in a eutrophic coastal lagoon in the oligotrophic Red Sea, which showed strong seasonality in terms of temperature (22.1–33.3 °C) and large phytoplankton blooms. Viral abundances ranged from 2.2 × 106 to 1.5 × 107 viruses mL−1 and were closely related to chlorophyll a (chl a) concentration. Observed high virus-to-bacterium ratio (VBR) (4–79; 16 ± 4 (SE)) suggests that phages exerted a tight control of their hosts as indicated by the significant decrease in bacterial abundance with increasing virus concentration. Heterotrophic bacterial abundance also showed a significant decrease with increasing temperature. However, viral abundance was not related to temperature changes and the interaction of water temperature, suggesting an indirect effect of temperature on decreased host abundance, which was observed at the end of the summertime. From the estimated burst size (BS), we observed lysogeny (undetectable to 29.1%) at low percentages of 5.0% ± 1.2 (SE) in half of the incubations with mitomycin C, while it increased to 23.9% ± 2.8 (SE) when the host abundance decreased. The results suggest that lytic phages predominate, switching to a moderate proportion of temperate phages when the host abundance reduces. [ABSTRACT FROM AUTHOR]

The viral haemorrhagic septicaemia virus (VHSV), a single-stranded negative-sense RNA novirhabdovirus affecting a wide range of marine and freshwater fish species, is a main concern for European rainbow trout ( Oncorhynchus mykiss ) fish farmers. Its genome is constituted by six genes, codifying five structural and one nonstructural proteins. Many studies have been carried out to determine the participation of each gene in the VHSV virulence, most of them based on genome sequence analysis and/or reverse genetics to construct specific mutants and to evaluate their virulence phenotype. In the present study, we have used a different approach with a similar aim: hypothesizing that a failure in any step of the replication cycle can reduce the virulence in vivo, we studied in depth the in vitro replication of VHSV in different cell lines, using sets of strains from different origins, with high, low and moderate levels of virulence for fish. The results demonstrated that several steps in the viral replication cycle could affect VHSV virulence in fish, including adsorption, RNA synthesis and morphogenesis (including viral release). Notably, differences among strains in any step of the replication cycle were mostly strain-specific and reflected only in part the in vivo phenotype (high and low virulent). Our data, therefore, support the need for further studies aimed to construct completely avirulent VHSV recombinants targeting a combination of genes rather than a single one in order to study the mechanisms of genes interplay and their effect on viral phenotype in vitro and in vivo.

Though microbial processes in the oxygen minimum zones (OMZs) of the Arabian Sea (AS) are well documented, prokaryote-virus interactions are less known. The present study was carried out to determine the potential physico-chemical factors influencing viral abundances and their life strategies (lytic and lysogenic) along the vertical gradient in the OMZ of the AS (southwest coast of India). Water samples were collected during the southwest monsoon (SWM) season in two consecutive years (2015 and 2016) from different depths, namely, the surface layer, secondary chlorophyll a maxima (~30–40 m), oxycline (~70–80 m), and hypoxic/suboxic layers (~200–350 m). The high viral abundances observed in oxygenated surface waters (mean ± SD = 6.1 ± 3.4 × 106 viral-like particles (VLPs) mL−1), drastically decreased with depth in the oxycline region (1.2 ± 0.5 × 106 VLPs mL−1) and hypoxic/suboxic waters (0.3 ± 0.3 × 106 VLPs mL−1). Virus to prokaryote ratio fluctuated in the mixed layer (~10) and declined significantly (p < 0.001) to 1 in the hypoxic layer. Viral production (VP) and frequency of virus infected cells (FIC) were maximum in the surface and minimum in the oxycline layer, whereas the viral lysis was undetectable in the suboxic/hypoxic layer. The detection of a high percentage of lysogeny in suboxic (48%) and oxycline zones (9–24%), accompanied by undetectable rates of lytic viral infection support the hypothesis that lysogeny may represent the major survival strategy for viruses in unproductive or harsh nutrient/host conditions in deoxygenated waters. [ABSTRACT FROM AUTHOR]

Advances in design and use of light-sensitive and light-emitting sensors have facilitated observation, measurement, and control of neuronal activities. Viruses are effective vectors for delivery of these valuable research tools to mammalian brains. Recombinant viruses are optimized to mediate regulatable, long-term, and cell-specific gene expression. Here, we describe production methods for three of the most commonly used types of recombinant viruses in neurobiology research: adeno-associated virus (AAV), retrovirus/lentivirus, and glycoprotein-deleted rabies virus. These viral constructs are frequently used for calcium imaging or to deliver neural tracers and optogenetic tools. Popular constructs are readily obtained commercially; however, customized virus production through commercial sources is time consuming and costly. This article aims to provide readers with detailed technical information for rapid production and validation of high-quality viral particles in a laboratory setting while highlighting advantages and limitations of each viral type. © 2019 by John Wiley & Sons, Inc., (© 2019 John Wiley & Sons, Inc.)