They have been named Tupanvirus Soda lake and Tupanvirus Deep ocean. These viruses discovered in Brazil have a more complete genetic arsenal than any other virus and even some bacteria.
The list of giant viruses is still growing almost fifteen years after the discovery of Mimivirus and several others thereafter. These giant viruses are so large that they are observable under an optical microscope, and usually infect amoebae. Their identification has created a real shake-up in the community of biologists. Their existence is pushing scientists to rethink the definition of life and its current distribution in three major orders (bacteria, eukaryotes, and archaea).
The two new viruses were discovered by Professor Bernard La Scola, UMR MEPHI (Microbe Evolution Phylogeny and Infection) of the University of Aix-Marseille (France) and of the IHU Mediterranean Infection, and his team.
A very complete genetic equipment
The two new viruses are related to Mimivirus and have been named Tupanvirus Soda lake, for the first one that was discovered in a soda lake in Brazil and Tupanvirus Deep ocean for the second which was found at 3000 meters depth in oceanic sediments off Brazil. They measure between 450 and 550 nanometers and “look a lot like Mimivirus but they have the distinction of having a long and wide tail whose function remains for the moment unknown,” says Bernard La Scola.
PROTEIN. But it is not their external appearance that baffles scientists the most. Genome analyzes of these viruses show that they contain genes similar to those of known viruses and organisms in all three domains of life. In fact, Turpanviruses are home to a large number of genes involved in the assembly of proteins including the genes necessary to build the 20 known amino acids. “They have a genetic translation equipment (namely to transform messenger RNA into proteins) unique in the viral world, much more imposing than some eukaryotes. To be autonomous, they are only lacking what makes up the ribosome, they also still need a host to synthesize their proteins,” explains the researcher.
Megaviruses with a larger genome than some bacteria
The identification of these two new giant viruses is “a new step in understanding the originality of these viruses”. Scientists are beginning to understand better “their equipment in original and very complete gene, their ability to be infected by small viruses and finally their defense mechanism to protect themselves”, adds Bernard La Scola. It appears more and more that these organisms are very different from classical viruses. In the 1950s, they were excluded from the realm of life because they do not meet certain criteria characterizing life: they cannot reproduce or synthesize proteins using the genetic machinery of a host cell unlike other living organisms. But among the giant viruses these distinctions lose some of their meaning. The two new Turpanviruses have more genetic material than some bacteria, and almost all the equipment needed for protein synthesis! Biologists have been considering since their discovery to classify them in a new branch of life, a fourth area. A debate is engaged in this direction but still far from being closed.