Fifteen years since the discovery of the Mimivirus, a virus so large it is can be seen with an optical microscope, a team of researchers have announced the discovery of two new types of virus in Brazil. They are so large and have such a complex genetic makeup that we may need to rethink everything we think we know about viruses.
Called the Tupanvirus Soda lake and the Tupanvirus Deep ocean, these two new virus strains do not pose any risk to humans. However, they have a more complete genetic arsenal than any other virus, putting into question how we even define what a virus is. These two strains evolve in extreme aquatic habitats: the first in a soda lake and the second 3,000 meters deep in ocean sediments. But they are not only among the largest viruses ever discovered: they also contain more proteins than any other virus discovered up to now. According to current thinking, viruses can only reproduce or synthetise proteins by using the genetic machinery of a host cell, contrary to other living organisms. But in this case, these distinctions don’t hold. The two new Tupanviruses have more genetic material than certain bacteria, and almost all the necessary equipment to synthesise proteins.
“They are very like the Mimivirus, but they have a long and wide tail whose function we don’t understand for the moment”, explains Bernard LaScola, a virologist in Aix-Marseilles University in France. Besides their enormous size -they measure between 450 and 550 nanometers -the genome analyses of these viruses also show that they contain a large number of genes involved in making proteins, including some of the genes necessary for the 20 known amino acids. They have translational genetic equipment that is unique in the viral world, much more than certain eukaryotes. All they need to be autonomous is that which makes up ribosome [which synthesises proteins], as they still need a host to synthesise their proteins”, explains the researcher.
In terms of protein synthesis, they have the “largest translational apparatus within the known virosphere”, adds the researcher. The identification of these two new giant viruses is “a new step in understanding the unique nature of these viruses”. At the more we learn about these giant viruses, the better we understand what they are capable of.
You can find all the details of this study in Nature Communications.