A long-term prospecting study on giant viruses in terrestrial and marine Brazilian biomes.

The discovery of mimivirus in 2003 prompted the search for novel giant viruses worldwide. Despite increasing interest, the diversity and distribution of giant viruses is barely known. Here, we present data from a 2012-2022 study aimed at prospecting for amoebal viruses in water, soil, mud, and sewage samples across Brazilian biomes, using Acanthamoeba castellanii for isolation. A total of 881 aliquots from 187 samples covering terrestrial and marine Brazilian biomes were processed. Electron microscopy and PCR were used to identify the obtained isolates. Sixty-seven amoebal viruses were isolated, including mimiviruses, marseilleviruses, pandoraviruses, cedratviruses, and yaraviruses. Viruses were isolated from all tested sample types and almost all biomes. In comparison to other similar studies, our work isolated a substantial number of Marseillevirus and cedratvirus representatives. Taken together, our results used a combination of isolation techniques with microscopy, PCR, and sequencing and put highlight on richness of giant virus present in different terrestrial and marine Brazilian biomes.

Gene duplication as a major force driving the genome expansion in some giant viruses.

IMPORTANCE: Giant viruses are noteworthy not only due to their enormous particles but also because of their gigantic genomes. In this context, a fundamental question has persisted: how did these genomes evolve? Here we present the discovery of cedratvirus pambiensis, featuring the largest genome ever described for a cedratvirus. Our data suggest that the larger size of the genome can be attributed to an unprecedented number of duplicated genes. Further investigation of this phenomenon in other viruses has illuminated gene duplication as a key evolutionary mechanism driving genome expansion in diverse giant viruses. Although gene duplication has been described as a recurrent event in cellular organisms, our data highlights its potential as a pivotal event in the evolution of gigantic viral genomes.

Yaravirus: A novel 80-nm virus infecting Acanthamoeba castellanii.

Here we report the discovery of Yaravirus, a lineage of amoebal virus with a puzzling origin and evolution. Yaravirus presents 80-nm-sized particles and a 44,924-bp dsDNA genome encoding for 74 predicted proteins. Yaravirus genome annotation showed that none of its genes matched with sequences of known organisms at the nucleotide level; at the amino acid level, six predicted proteins had distant matches in the nr database. Complimentary prediction of three-dimensional structures indicated possible function of 17 proteins in total. Furthermore, we were not able to retrieve viral genomes closely related to Yaravirus in 8,535 publicly available metagenomes spanning diverse habitats around the globe. The Yaravirus genome also contained six types of tRNAs that did not match commonly used codons. Proteomics revealed that Yaravirus particles contain 26 viral proteins, one of which potentially representing a divergent major capsid protein (MCP) with a predicted double jelly-roll domain. Structure-guided phylogeny of MCP suggests that Yaravirus groups together with the MCPs of Pleurochrysis endemic viruses. Yaravirus expands our knowledge of the diversity of DNA viruses. The phylogenetic distance between Yaravirus and all other viruses highlights our still preliminary assessment of the genomic diversity of eukaryotic viruses, reinforcing the need for the isolation of new viruses of protists.