Search Results (84)

Mechanisms for the maintenance of chronic viruses are poorly understood, particularly for archaeal viruses. Here, we identify the product of Sulfolobus spindle-shaped virus 1 (SSV1) ORF a291 as a putative virally encoded toxin required for growth inhibition but dispensable for viral replication and virion production. Viruses lacking ORF a291 replicated their genomes and formed morphologically normal spindle-shaped particles, yet failed to inhibit the growth of uninfected Saccharolobus solfataricus. Substitution of residues at a predicted N-terminal signal peptide cleavage site abolished growth suppression without affecting replication, suggesting that secretion is essential for toxin function. Despite primary sequence divergence among fusellovirus toxin candidates, analysis of protein structure predictions revealed a conserved hydrolase-like fold across SSV1, SSV9 and SSV10 toxins. These findings demonstrate functional separation of viral replication and host growth suppression and support a model in which chronic archaeal viruses modulate host competition through antagonistic factors. This work expands the known diversity of putative viral toxins and suggests that fuselloviruses employ conserved strategies to promote persistence in extreme environments. Full article

Bacteriophages infecting phytopathogenic bacteria represent promising alternatives for plant disease control; however, some groups, such as filamentous bacteriophages, remain comparatively underexplored. In this study, we present a comprehensive characterization of XaF13, a filamentous bacteriophage that infects Xanthomonas vesicatoria, the causal agent of bacterial spot disease in pepper. Morphological analysis revealed a flexible filamentous virion architecture consistent with members of the family Inoviridae. To refine its genomic features, the XaF13 genome was resequenced through a hybrid approach combining newly generated Oxford Nanopore long reads with previously available Illumina data, resulting in a revised genome of 6965 bp. Comparative genomic analysis and intergenomic similarity assessment revealed low nucleotide identity with related inoviruses, supporting the recognition of XaF13 as a putative novel species based on VIRIDIC species-level thresholds. Phylogenetic reconstruction based on the Zot-like protein placed XaF13 within a broader inovirus lineage and showed that it forms a distinct evolutionary branch. In addition, physicochemical assays revealed that XaF13 remains stable across a broad pH range and tolerates brief exposure to elevated temperatures, whereas chloroform treatment and UV-C radiation reduced viral infectivity over time. Overall, these findings highlight the genomic distinctiveness and in vitro physicochemical stability of XaF13, contribute to a better understanding of filamentous bacteriophage diversity and provide a basis for future studies on its ecological role and possible interactions with phytopathogenic bacteria. Full article

Foodborne pathogens of Enterobacteriaceae are becoming an increasing global concern, with multidrug-resistant strains posing significant risks to food safety and public health, especially in high-risk products like dairy. This research focused on isolating, biologically characterizing, and genomically profiling new bacteriophages that target key Enterobacteriaceae members as potential biocontrol agents. Eight phages were isolated from wastewater using four bacterial hosts and analyzed through transmission electron microscopy, one-step growth analysis, adsorption kinetics, host range evaluation, whole-genome sequencing, comparative genomics, phylogenetic analysis, proteomic profiling, and virion assembly pathway characterization. All eight isolates exhibited icosahedral heads with contractile tails typical of Myoviridae morphology, demonstrated broad-spectrum lytic activity against 21 bacterial strains (infectivity: 47.6–95.2%), showed high adsorption efficiencies (84.75–99.98%), and had burst sizes ranging from 11 to 166 particles per cell. Genome sizes varied from 103 to 170 kb with coding densities between 92–96%. Importantly, none contained antimicrobial resistance genes, virulence factors, or lysogeny-associated elements, confirming their strictly lytic lifestyles and favorable biosafety profiles. Phylogenetic and comparative analyses indicated mosaic genomic structures influenced by horizontal gene transfer rather than host phylogeny. These findings provide a robust biological and genomic basis for evaluating these phages as potentially safe and effective alternatives to antibiotics in controlling foodborne Enterobacteriaceae, pending further in situ validation. Full article

Persistent oncovirus infections account for 15–20% of the global cancer burden, driving multiple forms of human cancer. To maintain persistent infection and spread, oncoviruses drive alterations in host cell metabolism, immune signaling, and cell-to-cell communication throughout tumor microenvironments. Accumulating evidence has indicated that these alterations occur in conjunction with a range of organelle remodeling events that can differ between “dormant” viral latency and active lytic replication. Throughout each phase of infection, oncoviruses alter the morphology, composition, and function of organelles to promote cellular survival and proliferation, while periodically supporting viral replication. Here, we review oncovirus-driven organelle remodeling strategies across distinct infection states, including viral latency, reactivation from latency, and chronic active replication. We focus on the molecular mechanisms by which oncovirus-driven organelle remodeling promotes cellular transformation, impedes immune responses, and facilitates virion assembly and egress. We also draw parallels between remodeling strategies employed by oncogenic and oncomodulatory viruses, emphasizing broadly conserved mechanisms across cancer-associated infections. Lastly, we highlight how studies of oncovirus organelle remodeling are critical for discovering vulnerabilities in both oncogenic virus infection and viral oncogenesis, with therapeutic potential for multiple cancers. Full article

Multidrug-resistant (MDR) Escherichia coli (E. coli) at the poultry–human interface motivates evaluating strictly lytic bacteriophages as targeted biocontrol candidates. A lytic E. coli phage (GADS24) was isolated from poultry waste in Saudi Arabia. Plaque formation and host range were assessed against 10 clinical E. coli isolates. Virion morphology was examined by transmission electron microscopy (TEM). Whole-genome sequencing (Illumina) and annotation (Prokka/RAST) were followed by comparative genomics (BLASTn 2.15.0, ANI JSpeciesWS: 2014–2025 Ribocon GmbH—Version: 5.0.3, dDDH GGDC: GGDC 3.0 and phylogenetic/proteomic analyses for taxonomic placement. GADS24 formed clear plaques and lysed 5 of 10 clinical E. coli isolates tested. TEM revealed an icosahedral capsid (~72.6 nm) and a contractile tail (~131.7 nm), consistent with Tevenvirinae/Mosigvirus morphology. The dsDNA genome is 168,896 bp (GC 43.8%) with 268 predicted ORFs and two tRNA genes (tRNA-Arg and tRNA-Met); no lysogeny-related genes were detected. The closest relative was Escherichia phage JN02 (98.44% ANI; 57.8% dDDH), supporting assignment to Mosigvirus while indicating a genome-resolved distinct lineage. The genome is available in GenBank (OQ703618). GADS24 represents a genome-resolved, strictly lytic Mosigvirus with in vitro biocontrol-relevant phenotyping against E. coli, supporting follow-up development for poultry-associated infection control and deeper phage–host interaction studies. Full article

Presented here are additional explanations for five key points offered by Rojero et al. in their 2025 publication in this journal, regarding characteristics of hyper-aggressive phage 0524phi7-1. These are (i) that the “bypassing of the evolution of host resistance” has been seen in other phages, especially dual-receptor generalist phages; (ii) that the “clearing of semi-turbid plaques” could be due to a phenomenon known as lysis inhibition collapse, (iii) that the “formation of satellite plaques” is reminiscent of the morphology of plaques generated by phage T4 star mutants, (iv) that “multi-day plaque enlargement” has been seen in other phages such as phage T7 but may also be explained by other phenomena including endolysin release, (v) that suggestions of phage “swimming” could be explained by virion diffusion within empty volumes found within maturing bacterial lawns. In particular, phage plaques that display lysis inhibition can influence the surrounding bacterial lawn well beyond their visible region. This presumably occurs via a reaction–diffusion mechanism whose leading edge of virion diffusion fails to display lysis inhibition, but which leaves in its wake lysis-inhibited bacterial infections that may not lyse in a timely manner. Phage-infected bacteria thus may be found well beyond a plaque’s visible boundaries, along with diffusing endolysin. Full article

Objectives: The durability and breadth of neutralizing antibodies following SARS-CoV-2 mRNA vaccination remain incompletely understood. This study aimed to investigate how longitudinal changes in antibody isotype composition impact neutralization against structurally diverse SARS-CoV-2 variants. Methods: After screening a broader cohort of mRNA-vaccinated sera, time-matched samples collected one month (1 mpv) and three months post-vaccination (3 mpv) were selected for detailed analysis. Neutralization assays against live virus variants, enzyme-linked immunosorbent assays (ELISA), and immunogold electron microscopy were performed to assess antibody titers, isotype levels, and virion morphology. Results: Neutralization titers declined markedly at 3 mpv, particularly against immune-evasive variants. Notably, the Lambda variant showed disproportionately high sensitivity to early-phase sera despite its divergence from the vaccine strain. Antibody isotyping showed that IgA and IgM decreased over time, while IgG levels were relatively more sustained. Electron microscopy revealed broader virion size heterogeneity in Lambda (50–200 nm) compared to Wuhan (80–120 nm), potentially enhancing multivalent antibody engagement. Consistently, ELISA under reduced spike density conditions showed that IgA and IgM retained stronger binding than IgG. Conclusions: These findings indicate that the decline of IgA and IgM compromises neutralization breadth, especially against structurally divergent variants such as Lambda. Sustaining dynamic multivalent isotype responses that adapt to diverse spike morphologies may be critical for broad cross-variant immunity. Full article

Respiratory syncytial virus (RSV) is a major human respiratory pathogen, particularly affecting infants, the elderly, and immunocompromised individuals. RSV exists in both spherical and filamentous forms, with the filamentous morphology associated with enhanced infectivity and cell-to-cell spread. Here, we demonstrate that RhoA, a small GTPase involved in cytoskeletal regulation, is essential for filamentous RSV morphogenesis through its role in organizing lipid raft microdomains. Rhosin, a selective RhoA inhibitor developed through structure-guided screening, disrupts GEF–RhoA interactions to block RhoA activation. The pharmacological inhibition of RhoA with Rhosin significantly reduced filamentous virion formation, disrupted RSV fusion (F) protein colocalization with lipid rafts, and diminished cell-to-cell fusion, without affecting overall viral replication. Scanning electron microscopy revealed that Rhosin-treated infected HEp-2 cells exhibited fewer and shorter filamentous projections compared to the extensive filament formation seen in untreated cells. β-galactosidase-based fusion assays confirmed that reduced filamentation corresponded with decreased cell-to-cell fusion. The biophysical separation of RSV spherical and filamentous particles by sucrose gradient velocity sedimentation, coupled with fluorescence and transmission electron microscopy, showed that Rhosin treatment shifted virion morphology toward spherical forms. This suggests that RhoA activity is critical for filamentous virion assembly, which may enhance viral spread. Immunofluorescence microscopy using lipid raft-selective dyes (DiIC₁₆) and fusion protein-specific antibodies revealed the strong co-localization of RSV proteins with lipid rafts. Importantly, the pharmacological inhibition of RhoA with Rhosin disrupted F protein partitioning into raft domains, underscoring the requirement for intact lipid rafts in assembly. These findings highlight a novel role for host RhoA signaling in regulating viral assembly through raft microdomain organization, offering a potential target for host-directed antiviral intervention aimed at altering RSV structural phenotypes and limiting pathogenesis. Full article

The continued effective control of retroviral infections will no doubt require the development of new clinical interventions targeting underexploited areas of retroviral biology such as genome selection and virion assembly. In our previous work, we demonstrated that both the Gag-psi (Ψ) interaction and genomic RNA (gRNA) dimerization each uniquely contribute to the formation, morphology, and stability of Rous sarcoma virus (RSV) Gag-viral RNA (vRNA) biomolecular condensates (BMCs). The present work builds upon those observations, utilizing atomic force microscopy (AFM) and fluorescence correlation spectroscopy (FCS) to elucidate the nanoscale morphology, resistance to mechanical deformation, and constituent diffusivity of RSV Gag-vRNA BMCs. These approaches revealed a novel role for gRNA dimerization in nanoscale condensate architecture and mechanical stability that aids in our understanding of why gRNA dimerization is critical for efficient packaging of the retroviral genome. Further biophysical characterization of RSV Gag-gRNA BMCs therefore possesses great potential to reveal novel avenues for therapeutic intervention. Full article

Zaire Ebolavirus (EBOV) is one type of filovirus that causes the deadly EBOV disease, with an average fatality rate of around 50%. EBOV outbreaks are devastating and unpredictable and may emerge as the next global pandemic. As a BSL-4 pathogen, EBOV is inaccessible to regular biological laboratories. Therefore, EBOV virus-like particles (EBOV-VLPs) and EBOV pseudoviruses (EBOV-PVs) are utilized in the initial development of many potential therapies, for safety reasons and ease of procurement, as opposed to using infectious viruses. To investigate the host cell entry of EBOV and develop viral entry blockers, the EBOV model virions must accurately represent the morphological and mechanical properties of infectious EBOV virions. Due to the nanometer scale and irregular shape of EBOVs, these properties are challenging to characterize. In this research, state-of-the-art nanoscale characterization techniques are employed to examine the mechanical and structural elements of a selection of commonly used EBOV-approximating model virions. This study comprehensively determines the accuracy of EBOV approximation with a variety of model virions and the uniformity of mechanical and structural traits across different model virion types and preparation methods. This provides important implications for developing therapeutic treatments against EBOV using these model virions. Full article

Background: Seasonal influenza causes significant morbidity and mortality each year. Since viruses can easily acquire drug-resistant mutations, it is necessary to develop new antiviral strategies with different targets. Near-infrared photoimmunotherapy (NIR-PIT) is a type of anti-cancer therapy that has recently attracted considerable attention, with favorable outcomes reported for several cancers. In this study, we investigated whether this approach could be used as a novel anti-influenza therapy to destroy influenza virus and infected cells. Methods: To evaluate the efficacy of near-infrared antiviral photoimmunotherapy (NIR-AVPIT), we prepared an anti-hemagglutinin (HA) monoclonal antibody without neutralizing activity against influenza A virus (FluV) labeled with IR-700 and reacted it with FluV and infected cells, as well as HA-expressing HEK293 cells. Results: NIR-AVPIT strongly inactivated FluV virions, suppressed cytopathic effects, and achieved more than a 4-log reduction in viral RNA amplification. Treatment of FluV-infected cells with the antibody-IR700 complex and NIR in the early stages of infection significantly inhibited viral propagation, and double treatment with time apart exerted a greater inhibitory effect. NIR-AVPIT rapidly induced morphological changes in HA-expressing HEK293 cells and inhibited the proliferation of these cells. Conclusions: These results suggest that NIR-AVPIT targeting HA antigens could inactivate FluV and eliminate infected cells in vitro. This strategy is a promising approach to treat various viral infections, including influenza. Full article

Recently, using a panel of recombinant CHO cell lines, we identified the coxsackie and adenovirus receptor (CAR) and histo-blood group antigens (HBGAs) or sialic acid as the minimum requirement for susceptibility to rhesus enteric calicivirus (ReCV) infections. While ReCVs cause lytic infection in LLC-MK2 cells, recombinant CHO (rCHO) cell lines did not exhibit any morphological changes upon infection. To monitor infectious virus production, rCHO cell cultures had to be freeze–thawed and titrated on LLC-MK2 monolayers. This raised the question of whether ReCV infection in rCHO cells is persistent and whether non-enveloped progeny virions are released from the infected cells. Here, we used the rCHO-CAR+ cell line and a CAR and sialic acid-dependent recovirus strain (FT7) and found that these cells were persistently infected, and infectious virus was continuously produced and released into the culture without showing any visible cell damage. Viral capsid protein and replication intermediate double-stranded RNA (dsRNA) were detectable in almost all cells for at least 12 passages. We suspect a fully exosomal viral exit mechanism without a lytic cycle in these cells. rCHO cell may provide a valuable system for ReCV production (producer cell line) and serve as a model for investigating enteric calicivirus non-lytic viral exit mechanisms and the properties of the released, most likely membrane-cloaked, infectious progeny virions. Full article

Soybean bradyrhizobia (Bradyrhizobium spp.) are symbiotic root-nodulating bacteria that fix atmospheric nitrogen for the host plant. The University of Delaware Bradyrhizobium Culture Collection (UDBCC; 353 accessions) was created to study the diversity and ecology of soybean bradyrhizobia. Some UDBCC accessions produce temperate (lysogenic) bacteriophages spontaneously under routine culture conditions without chemical or other apparent inducing agents. Spontaneous phage production may promote horizontal gene transfer and shape bacterial genomes and associated phenotypes. A diverse subset (n = 98) of the UDBCC was examined for spontaneously produced virus-like particles (VLPs) using epifluorescent microscopy, with a majority (69%) producing detectable VLPs (>1 × 10⁷ mL⁻¹) in laboratory culture. Phages from the higher-producing accessions (>2.0 × 10⁸ VLP mL⁻¹; n = 44) were examined using transmission electron microscopy. Diverse morphologies were observed, including various tail types and lengths, capsid sizes and shapes, and the presence of collars or baseplates. In many instances, putative extracellular vesicles of a size similar to virions were also observed. Three of the four species examined (B. japonicum, B. elkanii, and B. diazoefficiens) produced apparently tailless phages. All species except B. ottawaense also produced siphovirus-like phages, while all but B. diazoefficiens additionally produced podovirus-like phages. Myovirus-like phages were restricted to B. japonicum and B. elkanii. At least three strains were polylysogens, producing up to three distinct morphotypes. These observations suggest spontaneously produced phages may play a significant role in the ecology and evolution of soybean bradyrhizobia. Full article

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel betacoronavirus, is the causative agent of COVID-19, which has caused economic and social disruption worldwide. To date, many drugs and vaccines have been developed for the treatment and prevention of COVID-19 and have effectively controlled the global epidemic of SARS-CoV-2. However, SARS-CoV-2 is highly mutable, leading to the emergence of new variants that may counteract current therapeutic measures. Electron microscopy (EM) is a valuable technique for obtaining ultrastructural information about the intracellular process of virus replication. In particular, EM allows us to visualize the morphological and subcellular changes during virion formation, which would provide a promising avenue for the development of antiviral agents effective against new SARS-CoV-2 variants. In this review, we present our recent findings using transmission electron microscopy (TEM) combined with electron tomography (ET) to reveal the morphologically distinct types of SARS-CoV-2 particles, demonstrating that TEM and ET are valuable tools for visually understanding the maturation status of SARS-CoV-2 in infected cells. This review also discusses the application of EM analysis to the evaluation of genetically engineered RNA viruses. Full article

Background: Antimicrobial-resistant bacteria represent a serious threat to public health. Among these bacteria, Salmonella is of high priority because of its morbidity levels and its ability to induce different types of cancer. Aim: This study aimed to identify Salmonella strains encoding genes linked to the promotion of precancerous lesions and to isolate a bacteriophage to evaluate its preclinical potential against these bacteria. Methodology: An epidemiological approach based on wastewater analysis was employed to isolate Salmonella strains and detect genes associated with the induction of precancerous lesions. Antimicrobial susceptibility was assessed by the disk diffusion method. A bacteriophage was isolated via the double agar technique, and its morphological characteristics, stability, host range, replication dynamics, and ability to control Salmonella under different conditions were evaluated. The bacteriophage genome was sequenced and analyzed using bioinformatics tools. Results: Thirty-seven Salmonella strains were isolated, seventeen of which contained the five genes associated with precancerous lesions’ induction. These strains exhibited resistance to multiple antimicrobials, including fluoroquinolones. A bacteriophage from the Autographiviridae family with lytic activity against 21 bacterial strains was isolated. This phage exhibited a 20 min replication cycle, releasing 52 ± 3 virions per infected cell. It demonstrated stability and efficacy in reducing the Salmonella concentration in simulated gastrointestinal conditions, and its genome lacked genes that represent a biosafety risk. Conclusion: This bacteriophage shows promising preclinical potential as a biotherapeutic agent against Salmonella. Full article