Search Results (11)

Translation is a sine qua non process for life as we know it. Translation factors (TFs) and tRNAs are rare among viruses but are commonly found in giant viruses of the class Megaviricetes. In this study, we explored the diversity and distribution of tRNAs in giant viruses that were isolated and replicated in amoebae (phylum Amoebozoa), and investigated the evolutionary history of TFs to gain insights into their origins in these viruses. We analyzed the genomes of 77 isolated giant viruses, 52 of which contained at least 1 tRNA. In most of these viruses, tRNA sequences are dispersed throughout the genome, except in Tupanviruses and Yasmineviruses, where most tRNAs are clustered in specific genomic islands. The tRNAs in giant viruses often contain introns, with 73.1% of the genomes exhibiting at least one intronic region in these genes. Codon usage bias (CUB) analysis of various giant viruses revealed at least two distinct patterns of codon preferences among closely related viruses. We did not observe a clear correlation between the presence of tRNAs and CUB in giant viruses. Due to the limited size of these genes, we could not confidently investigate their phylogenetic relationships. However, phylogenetic analysis of TFs found in giant viruses often position these viruses as sister groups or embedded between different eukaryotic taxa with high statistical support. Overall, our findings reinforce the complexity of key components of the translation apparatus in different members of Nucleocytoviricota isolated from different regions of Earth. Full article

Phaeoviruses (Phycodnaviridae) are large icosahedral viruses in the phylum Nucleocytoviricota with dsDNA genomes ranging from 160 to 560 kb, infecting multicellular brown algae (Phaeophyceae). The phaeoviral host range is broader than expected, not only infecting algae from the Ectocarpales but also from the Laminariales order. However, despite phaeoviral infections being reported globally, Norwegian kelp species have not been screened. A molecular analysis of cultured and wild samples of two economically important kelp species in Norway (Saccharina latissima and Laminaria hyperborea) revealed that phaeoviruses are recurrently present along the Norwegian coast. We found the viral prevalence in S. latissima to be significantly higher at the present time compared to four years ago. We also observed regional differences within older samples, in which infections were significantly lower in northern areas than in the south or the fjords. Moreover, up to three different viral sequences were found in the same algal individual, one of which does not belong to the Phaeovirus genus and has never been reported before. This master variant therefore represents a putative new member of an unclassified phycodnavirus genus. Full article

The aim of this study was to investigate the microbial diversity encompassing bacteria, fungi, and viruses within the composite microbial community associated with Aedes aegypti mosquitoes in Manado, Indonesia, using a whole-genome shotgun metagenomics approach. Female mosquitoes were collected and grouped into pools of 50 individuals, from which genomic DNA (gDNA) and RNA were extracted separately. Whole-genome shotgun metagenomics were performed on gDNA samples. The bioinformatics analysis encompassed quality assessment, taxonomic classification, and visualization. The evaluation of the microbial community entailed an assessment of taxa abundance and diversity using Kraken version 2.1.2. The study delineated the prevalence of dominant bacterial phyla, including Proteobacteria, with varying abundance of Firmicutes, Bacteroidota, and Actinobacteria, and notable occurrence of Tenericutes. Furthermore, the presence of the fungal phylum Ascomycota was also detected. Among the identified barcodes, Barcode04 emerged as the most abundant and diverse, while Barcode06 exhibited greater evenness. Barcode03, 05, and 07 displayed moderate richness and diversity. Through an analysis of the relative abundance, a spectrum of viruses within Ae. aegypti populations was unveiled, with Negarnaviricota constituting the most prevalent phylum, followed by Nucleocytoviricota, Uroviricota, Artverviricota, Kitrinoviricota, Peploviricota, Phixviricota, and Cossaviricota. The presence of Negarnaviricota viruses raises pertinent public health concerns. The presence of other viral phyla underscores the intricate nature of virus–mosquito interactions. The analysis of viral diversity provides valuable insights into the range of viruses carried by Ae. aegypti. The community exhibits low biodiversity, with a few dominant species significantly influencing its composition. This has implications for healthcare and ecological management, potentially simplifying control measures but also posing risks if the dominant species are harmful. This study enriches our comprehension of the microbiome and virome associated with Ae. aegypti mosquitoes, emphasizing the importance of further research to fully comprehend their ecological significance and impact on public health. The findings shed light on the microbial ecology of Ae. aegypti, offering potential insights into mosquito biology, disease transmission, and strategies for vector control. Future studies should endeavor to establish specific associations with Ae. aegypti, elucidate the functional roles of the identified microbial and viral species, and investigate their ecological implications. Full article

Our perception of viruses has been drastically evolving since the inception of the field of virology over a century ago. In particular, the discovery of giant viruses from the Nucleocytoviricota phylum marked a pivotal moment. Their previously concealed diversity and abundance unearthed an unprecedented complexity in the virus world, a complexity that called for new definitions and concepts. These giant viruses underscore the intricate interactions that unfold over time between viruses and their hosts, and are themselves suspected to have played a significant role as a driving force in the evolution of eukaryotes since the dawn of this cellular domain. Whether they possess exceptional relationships with their hosts or whether they unveil the actual depths of evolutionary connections between viruses and cells otherwise hidden in smaller viruses, the attraction giant viruses exert on the scientific community and beyond continues to grow. Yet, they still hold surprises. Indeed, the recent identification of mirusviruses connects giant viruses to herpesviruses, each belonging to distinct viral realms. This discovery substantially broadens the evolutionary landscape of Nucleocytoviricota. Undoubtedly, the years to come will reveal their share of surprises. Full article

Acanthamoeba polyphaga mimivirus, so called because of its “mimicking microbe”, was discovered in 2003 and was the founding member of the first family of giant viruses isolated from amoeba. These giant viruses, present in various environments, have opened up a previously unexplored field of virology. Since 2003, many other giant viruses have been isolated, founding new families and taxonomical groups. These include a new giant virus which was isolated in 2015, the result of the first co-culture on Vermamoeba vermiformis. This new giant virus was named “Faustovirus”. Its closest known relative at that time was African Swine Fever Virus. Pacmanvirus and Kaumoebavirus were subsequently discovered, exhibiting phylogenetic clustering with the two previous viruses and forming a new group with a putative common ancestor. In this study, we aimed to summarise the main features of the members of this group of giant viruses, including Abalone Asfarvirus, African Swine Fever Virus, Faustovirus, Pacmanvirus, and Kaumoebavirus. Full article

The global demand for industrial enzymes has been increasing in recent years, and the search for new sources of these biological products is intense, especially in microorganisms. Most known viruses have limited genetic machinery and, thus, have been overlooked by the enzyme industry for years. However, a peculiar group of viruses breaks this paradigm. Giant viruses of the phylum Nucleocytoviricota infect protists (i.e., algae and amoebae) and have complex genomes, reaching up to 2.7 Mb in length and encoding hundreds of genes. Different giant viruses have robust metabolic machinery, especially those in the Phycodnaviridae and Mimiviridae families. In this review, we present some peculiarities of giant viruses that infect protists and discuss why they should be seen as an outstanding source of new enzymes. We revisited the genomes of representatives of different groups of giant viruses and put together information about their enzymatic machinery, highlighting several genes to be explored in biotechnology involved in carbohydrate metabolism, DNA replication, and RNA processing, among others. Finally, we present additional evidence based on structural biology using chitinase as a model to reinforce the role of giant viruses as a source of novel enzymes for biotechnological application. Full article

We sequenced the complete mitogenomes, 18S and 28S rRNA of two new Scarites isolates, collected in Eastern Nebraska and Northern Arkansas (US). Based on molecular sequence data comparison and morphological characteristics, the new isolates were identified as a subspecies of Scarites subterraneus Fabricius 1775, for which we propose the subspecies names ‘nebraskensis’ and ‘arkansensis’. The new 18S and 28S rRNA sequences were found to be 99% and 98% identical to Scarites subterraneus. There are no other Scarites 18S or 28S rRNA sequences in the Genbank database, however, phylogenetic analysis of the Cox1 genes showed S. vicinus Chaudoir, 1843, and S. aterrimus Morawitz, 1863, as the closest relatives. This is the first report of a mitogenome for S. subterraneus, and only the second mitogenome for that genus. The nucleotide sequence identity between the mitogenomes of the two isolates is 98.8%, while the earlier sequenced S. buparius Forster 1771 mitogenome is more distantly related, with only 90% (to ssp. nebraskensis) and 89% (to ssp. arkansensis) overall nucleotide sequence identity. These new mitogenomes, and their phylogenetic analysis, firmly establish the position of Scarites on the Carabidae family tree and further refine the genus. In addition to the molecular data provided for the Scarites species, this approach also allowed us to identify bacterial and viral signatures for Providencia, Myroides, Spiroplasma, and a giant Nucleocytoviricota virus, associated with the Scarites species. We hereby present a simple and efficient protocol for identification and phylogenetic analysis of Scarites, that is applicable to other Coleoptera, based on total DNA extraction and Illumina short-read Next-Gen sequencing. Full article

The nucleocytoplasmic large DNA viruses (NCLDV) possess unique characteristics that have drawn the attention of the scientific community, and they are now classified in the phylum Nucleocytoviricota. They are characterized by sharing many genes and have their own transcriptional apparatus, which provides certain independence from their host’s machinery. Thus, the presence of a robust transcriptional apparatus has raised much discussion about the evolutionary aspects of these viruses and their genomes. Understanding the transcriptional process in NCLDV would provide information regarding their evolutionary history and a better comprehension of the biology of these viruses and their interaction with hosts. In this work, we reviewed NCLDV transcription and performed a comparative functional analysis of the groups of genes expressed at different times of infection of representatives of six different viral families of giant viruses. With this analysis, it was possible to observe a temporal profile of their gene expression and set of genes activated in specific phases throughout the multiplication cycle as a common characteristic of this group. Due to the lack of information regarding the transcriptional regulation process of this group of pathogens, we sought to provide information that contributes to and opens up the field for transcriptional studies of other viruses belonging to Nucleocytoviricota. Full article

Kaumoebavirus infects the amoeba Vermamoeba vermiformis and has recently been described as a distant relative of the African swine fever virus. To characterize the diversity and evolution of this novel viral genus, we report here on the isolation and genome sequencing of a second strain of Kaumoebavirus, namely LCC10. Detailed analysis of the sequencing data suggested that its 362-Kb genome is linear with covalently closed hairpin termini, so that DNA forms a single continuous polynucleotide chain. Comparative genomic analysis indicated that although the two sequenced Kaumoebavirus strains share extensive gene collinearity, 180 predicted genes were either gained or lost in only one genome. As already observed in another distant relative, i.e., Faustovirus, which infects the same host, the center and extremities of the Kaumoebavirus genome exhibited a higher rate of sequence divergence and the major capsid protein gene was colonized by type-I introns. A possible role of the Vermamoeba host in the genesis of these evolutionary traits is hypothesized. The Kaumoebavirus genome exhibited a significant gene strand bias over the two-third of genome length, a feature not seen in the other members of the “extended Asfarviridae” clade. We suggest that this gene strand bias was induced by a putative single origin of DNA replication located near the genome extremity that imparted a selective force favoring the genes positioned on the leading strand. Full article

The extension of virology beyond its traditional medical, veterinary, or agricultural applications, now called environmental virology, has shown that viruses are both the most numerous and diverse biological entities on Earth. In particular, virus isolations from unicellular eukaryotic hosts (heterotrophic and photosynthetic protozoans) revealed numerous viral types previously unexpected in terms of virion structure, gene content, or mode of replication. Complemented by large-scale metagenomic analyses, these discoveries have rekindled interest in the enigma of the origin of viruses, for which a description encompassing all their diversity remains not available. Several laboratories have repeatedly tackled the deep reconstruction of the evolutionary history of viruses, using various methods of molecular phylogeny applied to the few shared “core” genes detected in certain virus groups (e.g., the Nucleocytoviricota). Beyond the practical difficulties of establishing reliable homology relationships from extremely divergent sequences, I present here conceptual arguments highlighting several fundamental limitations plaguing the reconstruction of the deep evolutionary history of viruses, and even more the identification of their unique or multiple origin(s). These arguments also underline the risk of establishing premature high level viral taxonomic classifications. Those limitations are direct consequences of the random mechanisms governing the reductive/retrogressive evolution of all obligate intracellular parasites. Full article

Potassium ion (K⁺) channels have been observed in diverse viruses that infect eukaryotic marine and freshwater algae. However, experimental evidence for functional K⁺ channels among these alga-infecting viruses has thus far been restricted to members of the family Phycodnaviridae, which are large, double-stranded DNA viruses within the phylum Nucleocytoviricota. Recent sequencing projects revealed that alga-infecting members of Mimiviridae, another family within this phylum, may also contain genes encoding K⁺ channels. Here we examine the structural features and the functional properties of putative K⁺ channels from four cultivated members of Mimiviridae. While all four proteins contain variations of the conserved selectivity filter sequence of K⁺ channels, structural prediction algorithms suggest that only two of them have the required number and position of two transmembrane domains that are present in all K⁺ channels. After in vitro translation and reconstitution of the four proteins in planar lipid bilayers, we confirmed that one of them, a 79 amino acid protein from the virus Tetraselmis virus 1 (TetV-1), forms a functional ion channel with a distinct selectivity for K⁺ over Na⁺ and a sensitivity to Ba²⁺. Thus, virus-encoded K⁺ channels are not limited to Phycodnaviridae but also occur in the members of Mimiviridae. The large sequence diversity among the viral K⁺ channels implies multiple events of lateral gene transfer. Full article