João Victor Rodrigues Pessoa Carvalho

A novel chlorovirus was isolated from a freshwater sample collected from a Brazilian urban lake. Members of the family Phycodnaviridae, the chloroviruses have large linear dsDNA genomes (285–410 kbp) that encode hundreds of proteins and tRNAs. Despite their ecological and evolutionary importance, chloroviruses remain poorly studied, especially in South America. This study aimed to expand the understanding of this viral group by characterizing a new chlorovirus found in Brazil within a species-level framework. Following inoculation of algal cultures with environmental samples, plaque formation was observed 72 h after incubation on a Chlorella variabilis lawn. The new isolate was named BR-MG-N02. The virus remained stable across a temperature range of −30 °C to 37 °C, yet was highly sensitive to UV exposure. This virus has a capsid of approximately 160 nm and establishes a large viral factory in the host cytoplasm. Whole-genome hybrid sequencing revealed a 344,634 bp genome, containing 11 tRNAs and 389 protein-coding sequences. Phylogeny and comparative genomic analyses revealed that BR-MG-N02 is a new member of the species Chlorovirus americanus. We show that viruses belonging to this species harbor an extensive DNA methylation machinery, accounting for ~5% of their gene content and suggesting a potential for DNA methylation. Using representatives isolates, we present evidence of intraspecific differences in biological traits of these chloroviruses, as for burst size and plaque morphology. Altogether, our results expand current knowledge about the viral diversity in Brazil and provide valuable insights into the biology of giant algal viruses.

Chloroviruses are large double-stranded DNA (dsDNA) viruses that infect Chlorella -like green algae in freshwater environments. Despite being extensively studied in the Northern Hemisphere, little is known about their diversity and biology in tropical regions. In this study, we report the isolation and characterization of a novel chlorovirus, named Chlorovirus BR-MG-N01, infecting Chlorella variabilis NC64A. The virus was recovered from a freshwater lake in Guanhães, Minas Gerais, Brazil, located in a transition zone between the Atlantic Forest and Cerrado biomes. Electron microscopy revealed icosahedral particles of approximately 160 nm in diameter. The viral growth profile showed a 2-log increase after 24 h of infection. BR-MG-N01 demonstrated high thermal stability, remaining viable from −80°C to 56°C, but showed low tolerance to ultraviolet radiation, with a rapid decrease in titer after 3 min of exposure. Genome sequencing revealed a 318 kbp dsDNA genome containing 384 coding sequences. Gene annotation identified a high number of endonucleases, two of which are putatively novel, as well as genes related to transcription and oxidative stress resistance. Phylogenetic analysis based on the DNA polymerase gene placed BR-MG-N01 within the Alphachlorovirus subgenus, closely related to the species Chlorovirus vanettense . Comparative genomic analysis revealed strong synteny and high sequence similarity with other members of this species. The isolation of Chlorovirus BR-MG-N01 expands the known distribution of chloroviruses and highlights the need for further exploration of tropical environments to uncover the ecological and evolutionary diversity of these enigmatic aquatic viruses. IMPORTANCE: Chloroviruses are large dsDNA viruses that infect algae, with limited available research in tropical environments. This work helps address that gap by presenting the first detailed genomic and biological characterization of a native chlorovirus from Brazil. We show that Brazilian environments harbor viral lineages as complex and diverse as those described in well-studied regions of the Northern Hemisphere. By documenting the isolate’s morphology, stability, replication profile, genomic architecture, and evolutionary placement, this study establishes the basis for future ecological and evolutionary research on algal viruses in the country. Overall, the discovery highlights a hidden viral diversity in Brazilian ecosystems and reinforces the importance of investigating microorganisms from tropical and understudied habitats.

The monkeypox virus (MPXV) is an emerging zoonotic pathogen responsible for mpox, a disease characterized by some smallpox-like symptoms, typically mild but occasionally fatal. The largest mpox recorded global outbreak began in May 2022, with over 162,000 cases across 140 countries. Herein, we have analyzed the intra-clonal diversity of MPXV obtained from a single skin lesion sample from a male patient (June 2022). Three viral clones were obtained following phenotypic evaluation of MPXV lysis plaque characteristics over a three-course infection in BSC-40 cells. Unlike the vaccinia virus Western Reserve (VACV-WR) strain, MPXV clones did not produce comet-like structures, suggesting reduced extracellular enveloped virus (EEV) morphotype release, which is associated with viral dissemination. Whole-genome sequencing and assembly identified subtle differences among clones. Comparative genomic analyses, including synteny and single nucleotide variation (SNV) calling, revealed intra-clonal differences and divergence from clade I and II references, although the variety of mutations found did not reveal possible variations at the protein level. Altogether, these findings suggest that although similar, it is possible that distinct MPXV variants may circulate together and can be found in a single exanthematous lesion.

In recent decades, there has been an increased interest in viruses of microorganisms (VoM) and international efforts to gather researchers interested in them. Here, we describe the 1st Brazilian Symposium on Viruses of Microorganisms (BrVoM), held on 1 August 2025 at the Federal University of Minas Gerais (UFMG, Belo Horizonte, Brazil) with institutional support from the Federal University of Alfenas (UNIFAL) and the Brazilian Society for Virology (SBV). The symposium greatly surpassed expectations, gathering nearly 300 attendees from all Brazilian geographical regions. The scientific program included keynote and thematic lectures covering bacteriophages, fungal viruses, giant viruses, and microbial resources regulation. The event was remarkable for its collaborative spirit and inclusion of early career attendees. The success of this first edition highlights the vitality of the Brazilian community working on microbial viruses and sets the stage for future editions.

Marseilleviruses are giant viruses that infect amoebas and have been isolated from various environments. Here, we describe a new strain, isolated from a water sample collected from the Paraguay River in the Brazilian Pantanal, which we have named "Marseillevirus pantanense". Transmission and scanning electron microscopy revealed icosahedral particles approximately 190 nm in diameter. Genomic and phylogenetic analyses show that M. pantanense has a 379,900-bp genome with 496 open reading frames, including 12 ORFans and two tRNAs. Furthermore, phylogenetic analysis places M. pantanense within Marseillevirus lineage A, group I. The findings of in this study underscore the importance of isolating new viruses to expand our understanding of the abundance and distribution of giant viruses in Brazilian biomes.

The majority of giant algal viruses belong to the family Phycodnaviridae, class Algavirales, phylum Nucleocytoviricota. Among them, the genus Chlorovirus is the most studied, with three recognized groups based on genomics and host range, although many fundamental questions remain to be elucidated, particularly regarding their diversity. In this study, we focus on betachloroviruses, a poorly explored subgroup that infects the alga Micractinium conductrix Pbi. Here, we describe the isolation and genomic analysis of 11 new betachloroviruses from water samples collected in Nebraska, USA. With 25 fully sequenced genomes now available, we assessed the genomic diversity of these viruses. They have double-stranded DNA genomes ranging from 295 to 374 kbp, encoding hundreds of ORFs, of which a large number (~40%) lack known function. Comparative genomics and phylogenetic analyses revealed three species of betachlorovirus, each with high intra-species genomic identity. Notably, some isolates with over 99.5% genomic identity display markedly different plaque phenotypes, which led us to propose the use of the term genomovar among giant algal viruses, a concept potentially applicable to other giant viral groups yet to be explored. Altogether, this work advances our understanding of betachloroviruses and highlights the importance of linking viral genotype to phenotype, opening new avenues for exploring the diversity of giant algal viruses.

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.

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.