A Novel Brazilian Isolate Expands the Genomic and Phenotypic Characterization of Chlorovirus americanus

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.