The discovery of Acanthamoeba polyphaga Mimivirus, a giant amoeba-associated virus less than a decade ago, has shattered the definition of what is a virus. With an exceptional size of 500 nm, a genome of more than 1 Mb, a particle containing both DNA and RNA, possibility to be infected by another virus are unusual characteristics that make it immediately exceptional. Since then, several giant viruses have been isolated such as Marseillevirus. It is highly probable that closely related viruses will be isolated as it is now understood that they were not previously isolated because they are not filterable. Environmental metagenomic studies suggest that these viruses are ubiquitous. The discovery of virophages, small viruses able to infect Mimivirus as bacteriophage infect bacteria, fuel the debate about the nature of viruses and their place in the evolution of life. Current works, especially genome sequencing of these new viruses, open new perspectives about evolution and lateral gene transfer with their host but also with bacteria and other viruses. The knowledge about these viruses is only at the first step and increasing interest for it suggests that we are only at the dawn of the understanding of their role in evolution and ecosystems regulation.
Keywords: Acanthamoeba polyphaga Mimivirus; Marseillevirus; Mimivirus; NCLDV; giant virus; virophage.