The discovery of two giant viruses called Tupanviruses is described in a study published in Nature Communications this week. The viruses contain the most comprehensive set of genes necessary for protein assembly of all known viruses and provide insights into their evolution.
The discovery of giant viruses has sparked a debate on virus evolution, with two prominent theories. One possibility is that complex, giant viruses have evolved from a simple ancestor by acquiring genes from infected hosts. Alternatively, the ancestor of giant viruses may have already been a giant virus, and genes that were not required were lost over time.
Bernard La Scola and colleagues discovered the Tupanviruses in samples collected from a soda lake and deep ocean sediments in Brazil. Analyses of the genomes of these viruses show that they contain similar genes to those from known viruses and organisms from the three domains of life: archaea, bacteria and eukarya. However, homologues to about 30% of the genes have not been identified in other organisms. Compared to other viruses, the authors found that the Tupanviruses contain the largest set of genes involved in protein assembly and have genes necessary for incorporating all 20 amino acids into proteins. The origin of these 20 genes currently remains unclear.
Although further research will be necessary, the discovery of Tupanviruses provides an important step in understanding virus evolution, the authors conclude.