O isolamento e a caracterização genômica de novos isolados brasileiros do Reino Bamfordvirae expandem a diversidade e a taxonomia das famílias Marseilleviridae e Sputniviroviridae

Abstract

Giant amoeba viruses represent one of the most intriguing areas of modern virology, not only because of their complex morphology and genomes, but also because of their evolutionary and taxonomic relevance. These viruses are taxonomically classified in the Bamfordvirae kingdom, which is represented by different viral families, such as Marseilleviridae, Mimiviridae and Sputniviroviridae. Here, we describe new isolates of bamfordviruses obtained from Brazilian environmental samples. In the first part of the work, we describe Marseillevirus cajuinensis, the first isolation of a Marseilleviridae family virus from saltwater. This virus has a genome with approximately 380 thousand base pairs, containing 515 ORFs, including 38 ORFans, and a transfer RNA (tRNA) which was a gene, util then, rarely described among Marseilleviruses. Phylogenetic analyses showed that M. cajuinensis is a divergent member of lineage A and revealed that Marseilleviruses can be organized into three major groups instead of the classical five, suggesting the need for taxonomic reorganization. Based on these data, a proposal was submitted to the International Committee on Viral Taxonomy (ICTV) for the inclusion of new taxa in the Marseilleviridae family, including the creation of new species and genera to expand their taxonomical diversity. The second part of the work addresses the isolation of a tripartite viral system composed of a moumouvirus, a transpoviron and a new virophage, called Pantanal virophage, from samples collected in Pantanal biome region. Although phylogenetically grouped with Sputnikviruses, the Pantanal virophage presents distinct genomic characteristics, including three ORFans and exclusive genomic regions. The low nucleotide and amino acid identity in comparison with other members of the group added to the phylogeny of conserved proteins confirmed their divergence and supported their proposal as a new species within the genus Sputnikvirus. Altogether, the results reveal the importance of efforts to prospect and characterize new giant viruses and their associated elements, especially from ecosystems that have not yet been explored for this purpose, such as the Brazilian coast and Pantanal. The inclusion of these new isolates in comparative analyses allows for a deeper understanding of the evolutionary relationships between known viruses and highlights the ongoing need for review and updating of viral taxonomy, consolidating the role of these studies in expanding basic knowledge about viruses in the Bamfordvirae kingdom.