Viral Size Research Articles

The genome of a bunyavirus cannot be defined at the level of the viral particle but only at the scale of the viral population.

Bunyaviruses are enveloped negative or ambisense single-stranded RNA viruses with a genome divided into several segments. The canonical view depicts each viral particle packaging one copy of each genomic segment in one polarity named the viral strand. Several opposing observations revealed nonequal ratios of the segments, uneven number of segments per virion, and even packaging of viral complementary strands. Unfortunately, these observations result from studies often addressing other questions, on distinct viral species, and not using accurate quantitative methods. Hence, what RNA segments and strands are packaged as the genome of any bunyavirus remains largely ambiguous. We addressed this issue by first investigating the virion size distribution and RNA content in populations of the tomato spotted wilt virus (TSWV) using microscopy and tomography. These revealed heterogeneity in viral particle volume and amount of RNA content, with a surprising lack of correlation between the two. Then, the ratios of all genomic segments and strands were established using RNA sequencing and qRT-PCR. Within virions, both plus and minus strands (but no mRNA) are packaged for each of the three L, M, and S segments, in reproducible nonequimolar proportions determined by those in total cell extracts. These results show that virions differ in their genomic content but together build up a highly reproducible genetic composition of the viral population. This resembles the genome formula described for multipartite viruses, with which some species of the order Bunyavirales may share some aspects of the way of life, particularly emerging properties at a supravirion scale.

Determination of optimum nanofiltration conditions for the manufacturing process of human normal immunoglobulin G for intravenous administration

Scientific relevance. Medicinal products based on immunoglobulin class G (IgG) from human plasma are widely used in clinical practice to treat bacterial and viral infections, primary and secondary immunodeficiencies, and autoimmune diseases. Nanofiltration is a way to mitigate the risk of in-process contamination of raw materials with various pathogens, including viruses. Therefore, it is relevant to investigate the development and implementation of additional viral inactivation and/or elimination steps.Aim. This study aimed to develop and validate optimum nanofiltration conditions and to scale up the nanofiltration step for the manufacturing of human IgG for intravenous administration.Materials and methods. The study used a solution of IgG from plasma fractions II and III. The authors paired nanofilters manufactured by Planova 20N and BioEx (Asahi Kasei, Japan), Viresolve Pro (Merck Millipore, USA), Virosart HC and HF (Sartorius, Germany), and Pegasus SV4 and Prime (Pall, USA) with Sartopore polyethersulphone prefilters by Sartorius (Germany), Virosart MAX polyamide prefilters by Sartorius (Germany), and EKX-P regenerated cellulose prefilters by Pall (Germany). Virus reduction validation studies were performed with model viruses (human immunodeficiency virus type 1, porcine transmissible gastroenteritis virus, porcine parvovirus, murine encephalomyocarditis virus, and bovine viral diarrhoea virus) in the laboratories of the N.F. Gamaleya centre. The sample data analysis involved calculating mean values with 95% confidence intervals.Results. For all the selected combinations of prefilters and filters, the maximum nanofiltration throughput depended on the IgG concentration in the test solution. With the combination of an EKX-P filter with a Pegasus SV4 nanofilter, the maximum throughput and the IgG yield reached 6300 g/m2 and 95%, respectively. When combined with a Planova 20N nanofilter, EKX-P and Sartopore (polyethersulphone) filters provided a maximum throughput of up to 2980 g/m2 and an IgG yield of almost 100%, provided that the test solution had an IgG concentration of 10 g/L. With different filter combinations, virus reduction levels ranged from 4.00±0.05 to 4.75±0.04 log10 for human immunodeficiency virus type 1, from 4.30±0.04 to 4.55±0.06 log10 for porcine transmissible gastroenteritis virus, from 5.38±0.08 log10 to 5.57±0.04 log10 for murine encephalomyocarditis virus, 5.12±0.10 log10 to 5.25±0.08 log10 for porcine parvovirus, and exceeded 5.00 log10 for bovine viral diarrhoea virus. The virus reduction levels achieved were not statistically associated with prefilter brands.Conclusions. The study demonstrated that nanofiltration was effective at removing viruses with various virion sizes and physicochemical characteristics, including viruses as small as parvovirus B19. The levels of virus reduction exceeded 4 log10 and met the acceptance criteria.The laboratory-scale nanofiltration parameters and the corresponding filtration times, as well as IgG yields, did not change when the process was scaled up. Therefore, nanofiltration is an effective and productive technique that helps eliminate various types of viruses and considerably improve viral safety without affecting the quality of biological medicinal products.

Genetic and morphological characterization of a new genotype of nervous necrosis virus circulating among Nile tilapia in the south of Egypt.

Nervous necrosis virus (NNV) is the causative agent of viral nervous necrosis in freshwater and marine fishes. In this study, NNV circulating among wild and farmed Nile tilapia (Oreochromis niloticus) was genetically and morphologically characterized using reverse transcription polymerase chain reaction (RT-PCR), sequencing analysis, and transmission electron microscopy (TEM). Brain, eye, and other organ (spleen, kidney, heart, and liver) specimens were collected from 87 wild (66) and farmed (21) Nile tilapia fish during their adult or juvenile stage at different localities in Qena and Sohag governorates in southern Egypt. Among them, 57/87 fish showed suspected NNV clinical signs, and 30/87 were healthy. The results revealed that NNV was detected in 66 out of 87 fish (58.62% in the wild and 17.24% in farmed Nile tilapia by RT-PCR), and the prevalence was higher among diseased (55.17%) than in healthy (20.69%) fish. NNV was detected in the brain, eye, and other organs. Using TEM, virion size variations based on the infected organs were observed. Nucleotide sequence similarity indicated that NNVs had a divergence of 75% from other fish nodaviruses sequenced in Egypt and worldwide. Phylogenetic analysis distinguished them from other NNV genotypes, revealing the emergence of a new NNV genotype in southern Egypt. In conclusion, NNV is circulating among diseased and healthy Nile tilapia, and a new NNV genotype has emerged in southern Egypt.

Characterization and application of a lytic jumbo phage ZPAH34 against multidrug-resistant Aeromonas hydrophila.

Aeromonas hydrophila is an emerging foodborne pathogen causing human gastroenteritis. Aeromonas species isolated from food such as seafood presented multidrug-resistance (MDR), raising serious concerns regarding food safety and public health. The use of phages to infect bacteria is a defense against drug-resistant pathogens. In this study, phage ZPAH34 isolated from the lake sample exerted lytic activity against MDR A. hydrophila strain ZYAH75 and inhibited the biofilm on different food-contacting surfaces. ZPAH34 has a large dsDNA genome of 234 kb which belongs to a novel jumbo phage. However, its particle size is the smallest of known jumbo phages so far. Based on phylogenetic analysis, ZPAH34 was used to establish a new genus Chaoshanvirus. Biological characterization revealed that ZPAH34 exhibited wide environmental tolerance, and a high rapid adsorb and reproductive capacity. Food biocontrol experiments demonstrated that ZPAH34 reduces the viable count of A. hydrophila on fish fillets (2.31 log) and lettuce (3.28 log) with potential bactericidal effects. This study isolated and characterized jumbo phage ZPAH34 not only enriched the understanding of phage biological entity diversity and evolution because of its minimal virion size with large genome but also was the first usage of jumbo phage in food safety to eliminate A. hydrophila.

BIOLOGICAL FEATURES OF THE SARS-COV-2 VIRUS FROM DOMESTIC ANIMALS IN THE TERRITORY OF THE RK

There are limited data in the literature on the infection of domestic animals with SARS-CoV-2. Therefore, this article investigated biological samples (28 samples) taken from domestic animals on the territory of the Republic of Kazakhstan as part of a monitoring study. Using the ALPREP kit, total RNA was isolated by magnetic sorption, and using the ALSENSE-SARS-Cov-2 - RT-qPCR kit, the SARS-Cov-2 virus was detected from 7 samples. The SARS-Cov-2 virus was cultivated by the in vitro method on a Vero cell culture, and the biological activity of the accumulated virus-containing suspension was determined by the Reed and Muench method. A micrograph was taken on an electron microscope, which was used to determine the virus's size, shape and structure. As a result, a virus-containing suspension with the biological activity of 5.83±0.08 TCD50/cm3 was obtained on a Vero cell culture. The data obtained again indicates that domestic animals can also suffer from coronavirus and be carriers of this disease. It is becoming increasingly clear that the virus can infect and multiply in the organs of various farm and domestic animals.

Evolution of giant pandoravirus revealed by CRISPR/Cas9

Giant viruses (GVs) are a hotspot of unresolved controversies since their discovery, including the definition of “Virus” and their origin. While increasing knowledge of genome diversity has accumulated, GV functional genomics was largely neglected. Here, we describe an experimental framework to genetically modify nuclear GVs and their host Acanthamoeba castellanii using CRISPR/Cas9, shedding light on the evolution from small icosahedral viruses to amphora-shaped GVs. Ablation of the icosahedral major capsid protein in the phylogenetically-related mollivirus highlights a transition in virion shape and size. We additionally demonstrate the existence of a reduced core essential genome in pandoravirus, reminiscent of their proposed smaller ancestors. This proposed genetic expansion led to increased genome robustness, indicating selective pressures for adaptation to uncertain environments. Overall, we introduce new tools for manipulation of the unexplored genome of nuclear GVs and provide experimental evidence suggesting that viral gigantism has aroused as an emerging trait.

Electrospun membranes filtering 100nm particles from air flow by means of the van der Waals and Coulomb forces.

Nonwoven fibrous filter membranes are widely used in filtration because of their low cost. They are less effective in intercepting airborne particles of the order of 100nm, which is of the SARS-CoV-2 (COVID-19) virus's size. Many diseases, including COVID-19, predominantly spread by droplets released by breathing, coughing, sneezing, or medical procedures. It was shown that the smallest droplets can evaporate in air before settling, thus, making viruses airborne and easily penetrating even the best masks and filters. As a result, air-filtering membranes, which are capable of effective interception of ∼100nm nanoparticles are highly desirable. A traditional way to improve filtration efficiency by overlapping several layers of nonwoven fabrics increases the required pressure drop, and thus, should be avoided as much as possible. Here, we propose and demonstrate an innovative approach to enhance performance of filtration membranes based on (i) a dramatic reduction in the fiber size, and (ii) metal coating of the fibers. The first component of this approach allows one to incorporate a novel physical mechanism of filtration, the short-range van der Waals forces, whereas the second one adds the long-range electric Coulomb forces if the oncoming nanoparticles are pre-charged and the metal-plated membrane grounded. In the present work, the ∼100nm aluminum nanoparticles are filtered as a model of commensurate airborne single COVID-19 viruses, and Platinum is used as the sputter-coated material for the fiber coating. The resulting filtration efficiency enhanced by the electric Coulomb forces alone is increased by the factor of 1.77, while the filtration efficiency additionally facilitated by the van der Waals forces increased by the factor of 2.44. In comparison to the filter membranes with ∼500nm fibers without the electric forces involved, the van-der-Waals-electric filter membrane with fibers ∼90nm is 2.24 1.77=3.96 times more effective. The quality factor of a membrane which combines the van der Waals and Coulomb forces is 10.6 psi-1, which is almost three times that of a comparable membrane without the electric Coulomb force (with only van der Waals forces being used).

Incomplete tricarboxylic acid cycle and proton gradient in Pandoravirus massiliensis: is it still a virus?

The discovery of Acanthamoeba polyphaga Mimivirus, the first isolated giant virus of amoeba, challenged the historical hallmarks defining a virus. Giant virion sizes are known to reach up to 2.3 µm, making them visible by optical microscopy. Their large genome sizes of up to 2.5 Mb can encode proteins involved in the translation apparatus. We have investigated possible energy production in Pandoravirus massiliensis. Mitochondrial membrane markers allowed for the detection of a membrane potential in purified virions and this was enhanced by a regulator of the tricarboxylic acid cycle but abolished by the use of a depolarizing agent. Bioinformatics was employed to identify enzymes involved in virion proton gradient generation and this approach revealed that eight putative P. massiliensis proteins exhibited low sequence identities with known cellular enzymes involved in the universal tricarboxylic acid cycle. Further, all eight viral genes were transcribed during replication. The product of one of these genes, ORF132, was cloned and expressed in Escherichia coli, and shown to function as an isocitrate dehydrogenase, a key enzyme of the tricarboxylic acid cycle. Our findings show for the first time that a membrane potential can exist in Pandoraviruses, and this may be related to tricarboxylic acid cycle. The presence of a proton gradient in P. massiliensis makes this virus a form of life for which it is legitimate to ask the question “what is a virus?”.

The Secret Life of Giant Viruses in the California Current.

ABSTRACTIn the last few decades, the virology field has experienced a revolution in knowledge related to viral richness, diversity, and distribution in the oceans. Metagenomics associated with virus isolation methods have contributed to outstanding discoveries in marine virology. Giant viruses and other protist-infecting viruses belonging to the phylum Nucleocytoviricota have raised fundamental questions such as “what are the limits of virion size?”, “what is a viral genome able to encode?”, and “what is the ecological role of giant viruses in the ocean?” In a recent paper published in mSystems by Ha, Moniruzzaman, and Aylward (mSystems 6:e00293-21, 2021, https://doi.org/10.1128/mSystems.00293-21), the authors demonstrated by metatranscriptomic-related analyses that giant viruses are active members of the California Current microbial community, replicating, modulating, and exchanging genes with their protist hosts. This work not only explores the dynamics of giant virus gene expression in a natural environment but also reveals that nucleocytoviricotal abundance and ecological importance are underestimated.

SARS-CoV-2 Disinfection of Air and Surface Contamination by TiO2 Photocatalyst-Mediated Damage to Viral Morphology, RNA, and Protein.

SARS-CoV-2 is the causative agent of COVID-19, which is a global pandemic. SARS-CoV-2 is transmitted rapidly via contaminated surfaces and aerosols, emphasizing the importance of environmental disinfection to block the spread of virus. Ultraviolet C radiation and chemical compounds are effective for SARS-CoV-2 disinfection, but can only be applied in the absence of humans due to their toxicities. Therefore, development of disinfectants that can be applied in working spaces without evacuating people is needed. Here we showed that TiO2-mediated photocatalytic reaction inactivates SARS-CoV-2 in a time-dependent manner and decreases its infectivity by 99.9% after 20 min and 120 min of treatment in aerosol and liquid, respectively. The mechanistic effects of TiO2 photocatalyst on SARS-CoV-2 virion included decreased total observed virion count, increased virion size, and reduced particle surface spike structure, as determined by transmission electron microscopy. Damage to viral proteins and genome was further confirmed by western blotting and RT-qPCR, respectively. The multi-antiviral effects of TiO2-mediated photocatalytic reaction implies universal disinfection potential for different infectious agents. Notably, TiO2 has no adverse effects on human health, and therefore, TiO2-induced photocatalytic reaction is suitable for disinfection of SARS-CoV-2 and other emerging infectious disease-causing agents in human habitation.

Genetic diversity of porcine circovirus

This article is dedicated to the species diversity of porcine Circovirus that has been the causative agent of a disease caused by Porcine Circovirus widespread in pig farms of the Russian Federation and worldwide. The disease caused by porcine circovirus type II (PCV2) has various clinical signs accompanied by a number of syndromes as Postweaning multisystem wasting syndrome (SPMD), piglet dermatitis and nephropathy (SDNP), lymphoid, respiratory and reproductive dysfunctions and lesions in the central nervous system and gastrointestinal tract. The historical information in the review reflects the stages of porcine circovirus study, its first discovery, isolation in porcine kidney cell culture and identification of new nucleotide sequences of the virus. The presented data demonstrate the genetic differences of the viral genome, as well as the divergence in the clinics depending on the level of pathogenicity of the strains. Data of the previously unknown genotypes of Circovirus the study of their genetic sequences and the features of their distribution are presented in the article. The data on the genetic organization of porcine circovirus, its structure, virion size and nucleotide sequence length are illuminated in the article. Information was collected on the number of reading frames in the genomes of different types of circovirus, the sizes of capsid and replicative proteins, as well as their functions and influence on immune responses in the host organism, are given. It has been noted that an increase in the number of genotypes directly depends on the mutation of the capsid proteins of the circovirus. The data of phylogenetic analysis of porcine circovirus type 2 has been analyzed and in accordance with six genotypes of the virus has been identified (PCV-2a, PCV-2b, PCV-2c, PCV-2d, PCV-2e and PCV-2f). The prevalence of genotypes in the territory of the Russian Federation is provided. According to the retrospective analysis shifts in the genotypes of the virus with an increase in the virulence of the strains has been detected. It became possible to trace the distribution of genotypes across the territories of different countries, as well as to determine the prevailing types of porcine circovirus characteristic of these geographic areas as a result of the study.

Host Range and Coding Potential of Eukaryotic Giant Viruses.

Giant viruses are a group of eukaryotic double-stranded DNA viruses with large virion and genome size that challenged the traditional view of virus. Newly isolated strains and sequenced genomes in the last two decades have substantially advanced our knowledge of their host diversity, gene functions, and evolutionary history. Giant viruses are now known to infect hosts from all major supergroups in the eukaryotic tree of life, which predominantly comprises microbial organisms. The seven well-recognized viral clades (taxonomic families) have drastically different host range. Mimiviridae and Phycodnaviridae, both with notable intrafamilial genome variation and high abundance in environmental samples, have members that infect the most diverse eukaryotic lineages. Laboratory experiments and comparative genomics have shed light on the unprecedented functional potential of giant viruses, encoding proteins for genetic information flow, energy metabolism, synthesis of biomolecules, membrane transport, and sensing that allow for sophisticated control of intracellular conditions and cell-environment interactions. Evolutionary genomics can illuminate how current and past hosts shape viral gene repertoires, although it becomes more obscure with divergent sequences and deep phylogenies. Continued works to characterize giant viruses from marine and other environments will further contribute to our understanding of their host range, coding potential, and virus-host coevolution.

Modern taxonomy of viruses of vertebrates

The modern taxonomy of viruses of vertebrates is presented according to the information of ICTV issue 07.2019, ratification 03.2020. The leading criteria of taxonomy of viruses are named: type and structure of viral genome, mechanism of replication and morphology of virion. The periods of formation of taxonomic ranks of viruses are characterized: in 1966–1970 genera of viruses were formed, in 1971–1975 – families and subfamilies, since 1990 – orders, in 2018–2019 – realms, kingdoms, phylums, subphylums, classes, suborders, subgenеres. The nomenclature of viruses is described. Viruses belong to the Viruses domain. Viruses of vertebrates (1878 species) belong to 4 realms, 5 kingdoms, 10 phylums, 2 subphylums, 20 classes, 26 orders, 3 suborders, 45 families (of which 15 – DNA-genomic and 30 – RNA-genomic), 33 subfamilies, 345 genera and 49 subgenera. Taxonomic ranks of DNA- and RNA-genomic viruses of vertebrates are described. The DNA-genome family Anelloviridae and the unclassified RNA-genomic genus Deltavirus are not included in any realm. The family Birnaviridae is not classified within the kingdom Orthornavirae. The family of DNA-genomic Hepadnaviridae is included in the realm of RNA-containing viruses Riboviria on the grounds that the replication of hepadnaviruses occurs through the stage of RNA on the principle of reverse transcription, as in the family Retroviridae. The main taxonomic features of DNA- and RNA-genomic viruses of vertebrates are described: type and structure of viral genome (DNA or RNA, number of strands, conformation, fragmentation, polarity), shape and size of virions, presence of outer lipoprotein shell, type of capsid symmetry (spiral, iсosahedral). Some families, in addition to viruses of vertebrates, contain viruses of invertebrates and plants, in particular: families Poxviridae, Iridoviridae, Parvoviridae, Circoviridae, Smacoviridae, Genomoviridae, Rhabdoviridae, Nyamiviridae, Peribunyaviridae, Phenuiviridae, Nairoviviridae, Nodaviridae, Reoviridae and Birnaviridae – viruses of insects; families Genomoviridae, Rhabdoviridae, Phenuiviridae and Reoviridae – viruses of plants; family Nyamiviridae – viruses of nematodes, cestodes, sipunculidеs and echinoderms; family Rhabdoviridae – viruses of nematodes; family Reoviridae – Eriocheir sinensis reovirus; family Birnaviridae – viruses of tellines and rotifers.

Fluorescence Microscopy of the HIV-1 Envelope.

Human immunodeficiency virus (HIV) infection constitutes a major health and social issue worldwide. HIV infects cells by fusing its envelope with the target cell plasma membrane. This process is mediated by the viral Env glycoprotein and depends on the envelope lipid composition. Fluorescent microscopy has been employed to investigate the envelope properties, and the processes of viral assembly and fusion, but the application of this technique to the study of HIV is still limited by a number of factors, such as the small size of HIV virions or the difficulty to label the envelope components. Here, we review fluorescence imaging studies of the envelope lipids and proteins, focusing on labelling strategies and model systems.

How virus size and attachment parameters affect the temperature sensitivity of virus binding to host cells: Predictions of a thermodynamic model for arboviruses and HIV

Virus binding to host cells involves specific interactions between viral (glyco)proteins (GP) and host cell surface receptors (Cr) (protein or sialic acid (SA)). The magnitude of the enthalpy of association changes with temperature according to the change in heat capacity (ΔCp) on GP/Cr binding, being little affected for avian influenza virus (AIV) haemagglutinin (HA) binding to SA (ΔCp = 0 kJ/mol/K) but greatly affected for HIV gp120 binding to CD4 receptor (ΔCp = −5.0 kJ/mol/K). A thermodynamic model developed here predicts that values of ΔCp from 0 to ~−2.0 kJ/mol/K have relatively little impact on the temperature sensitivity of the number of mosquito midgut cells with bound arbovirus, while intermediate values of ΔCp of ~−3.0 kJ/mol/K give a peak binding at a temperature of ~20 °C as observed experimentally for Western equine encephalitis virus. More negative values of ΔCp greatly decrease arbovirus binding at temperatures below ~20 °C. Thus to promote transmission at low temperatures, arboviruses may benefit from ΔCp ~ 0 kJ/mol/K as for HA/SA and it is interesting that bluetongue virus binds to SA in midge midguts. Large negative values of ΔCp as for HIV gp120:CD4 diminish binding at 37 °C. Of greater importance, however, is the decrease in entropy of the whole virus (ΔSa_immob) on its immobilisation on the host cell surface. ΔSa_immob presents a repulsive force which the enthalpy-driven GP/Cr interactions weakened at higher temperatures struggle to overcome. ΔSa_immob is more negative (less favourable) for larger diameter viruses which therefore show diminished binding at higher temperatures than smaller viruses. It is proposed that small size phenotype through a less negative ΔSa_immob is selected for viruses infecting warmer hosts thus explaining the observation that virion volume decreases with increasing host temperature from 0 °C to 40 °C in the case of dsDNA viruses. Compared to arboviruses which also infect warm-blooded vertebrates, HIV is large at 134 nm diameter and thus would have a large negative ΔSa_immob which would diminish its binding at human body temperature. It is proposed that prior non-specific binding of HIV through attachment factors takes much of the entropy loss for ΔSa_immob so enhancing subsequent specific gp120:CD4 binding at 37 °C. This is consistent with the observation that HIV attachment factors are not essential but augment infection. Antiviral therapies should focus on increasing virion size, for example through binding of zinc oxide nanoparticles to herpes simplex virus, hence making ΔSa_immob more negative, and thus reducing binding affinity at 37 °C.

Diversity of Viruses Infecting Eukaryotic Algae.

Algae are photosynthetic organisms that drive aquatic ecosystems, e.g. fuelling food webs or forming harmful blooms. The discovery of viruses that infect eukaryotic algae has raised many questions about their influence on aquatic primary production and their role in algal ecology and evolution. Although the full extent of algal virus diversity is still being discovered, this review summarizes current knowledge of this topic. Where possible, formal taxonomic classifications are referenced from the International Committee on Taxonomy of Viruses (ICTV); since the pace of virus discovery has far surpassed the rate of formal classification, however, numerous unclassified viruses are discussed along with their classified relatives. In total, we recognized 61 distinct algal virus taxa with highly variable morphologies that include dsDNA, ssDNA, dsRNA, and ssRNA genomes ranging from approximately 4.4 to 560 kb, with virion sizes from approximately 20 to 210nm in diameter. These viruses infect a broad range of algae and, although there are a few exceptions, they are generally lytic and highly species or strain specific. Dedicated research efforts have led to the appreciation of algal viruses as diverse, dynamic, and ecologically important members of the biosphere, and future investigations will continue to reveal the full extent of their diversity and impact.

Visualizing the Transport of Porcine Reproductive and Respiratory Syndrome Virus in Live Cells by Quantum Dots-Based Single Virus Tracking.

Quantum dots (QDs)-based single particle analysis technique enables real-time tracking of the viral infection in live cells with great sensitivity over a long period of time. The porcine reproductive and respiratory syndrome virus (PRRSV) is a small virus with the virion size of 40-60nm which causes great economic losses to the swine industry worldwide. A clear understanding of the viral infection mechanism is essential for the development of effective antiviral strategies. In this study, we labeled the PRRSV with QDs using the streptavidin-biotin labeling system and monitored the viral infection process in live cells. Our results indicated that the labeling method had negligible effect on viral infectivity. We also observed that prior to the entry, PRRSV vibrated on the plasma membrane, and entered the cells via endosome mediated cell entry pathway. Viruses moved in a slow-fast-slow oscillatory movement pattern and finally accumulated in a perinuclear region of the cell. Our results also showed that once inside the cell, PRRSV moved along the microtubule, microfilament and vimentin cytoskeletal elements. During the transport process, virus particles also made contacts with non-muscle myosin heavy chain II-A (NMHC II-A), visualized as small spheres in cytoplasm. This study can facilitate the application of QDs in virus infection imaging, especially the smaller-sized viruses and provide some novel and important insights into PRRSV infection mechanism.

VB_PaeM_MIJ3, a Novel Jumbo Phage Infecting Pseudomonas aeruginosa, Possesses Unusual Genomic Features.

Phages are the most abundant biological entity on Earth. There are many variants in phage virion sizes, morphology, and genome sizes. Large virion sized phages, with genome sizes greater than 200 kbp have been identified and termed as Jumbo phages. These phages exhibit certain characteristics that have not been reported in phages with smaller genomes. In this work, a jumbo phage named MIJ3 (vB_PaeM_MIJ3) that infects Pseudomonas aeruginosa PAO1 was isolated from an equine livery yard in Leicestershire, United Kingdom. The genome and biological characteristics of this phage have been investigated. MIJ3 is a Myovirus with multiple long tail fibers. Assessment of the host range of MIJ3 revealed that it has the ability to infect many clinical isolates of P. aeruginosa. Bioinformatics analysis of the phage genome indicated that MIJ3 is closely related to the Pseudomonas phage, PA5oct. MIJ3 possesses several unusual features that are either rarely present in other phages or have not yet been reported. In particular, MIJ3 encodes a FtsH-like protein, and a putative lysidine synthase, TilS. These two proteins have not been reported in phages. MIJ3 also possesses a split DNA polymerase B with a novel intein. Of particular interest, unlike other jumbo phages infecting Pseudomonas spp., MIJ3 lacks the genetic elements required for the formation of the phage nucleus, which was believed to be conserved across jumbo Pseudomonas phages.

Discovery and Further Studies on Giant Viruses at the IHU Mediterranee Infection That Modified the Perception of the Virosphere.

The history of giant viruses began in 2003 with the identification of Acanthamoeba polyphaga mimivirus. Since then, giant viruses of amoeba enlightened an unknown part of the viral world, and every discovery and characterization of a new giant virus modifies our perception of the virosphere. This notably includes their exceptional virion sizes from 200 nm to 2 µm and their genomic complexity with length, number of genes, and functions such as translational components never seen before. Even more surprising, Mimivirus possesses a unique mobilome composed of virophages, transpovirons, and a defense system against virophages named Mimivirus virophage resistance element (MIMIVIRE). From the discovery and isolation of new giant viruses to their possible roles in humans, this review shows the active contribution of the University Hospital Institute (IHU) Mediterranee Infection to the growing knowledge of the giant viruses’ field.

The number of genes encoding repeat domain-containing proteins positively correlates with genome size in amoebal giant viruses.

Curiously, in viruses, the virion volume appears to be predominantly driven by genome length rather than the number of proteins it encodes or geometric constraints. With their large genome and giant particle size, amoebal viruses (AVs) are ideally suited to study the relationship between genome and virion size and explore the role of genome plasticity in their evolutionary success. Different genomic regions of AVs exhibit distinct genealogies. Although the vertically transferred core genes and their functions are universally conserved across the nucleocytoplasmic large DNA virus (NCLDV) families and are essential for their replication, the horizontally acquired genes are variable across families and are lineage-specific. When compared with other giant virus families, we observed a near–linear increase in the number of genes encoding repeat domain-containing proteins (RDCPs) with the increase in the genome size of AVs. From what is known about the functions of RDCPs in bacteria and eukaryotes and their prevalence in the AV genomes, we envisage important roles for RDCPs in the life cycle of AVs, their genome expansion, and plasticity. This observation also supports the evolution of AVs from a smaller viral ancestor by the acquisition of diverse gene families from the environment including RDCPs that might have helped in host adaption.