show Abstracthide AbstractSince the discovery of the very first giant virus, many kinds of giant viruses has been found and isolated from different kinds of aquatic environments. These giant enigmas have gained a lot of spotlight in the recent years, and have been investigated most especially on their ecological roles and mechanisms of infection. However, there remains the question of why giant viruses maintain and keep a large size as well as a large genome, when they are obligate parasites. Here we have isolated different Marseillevirus and sequenced its genomes, in the hopes of gaining insight on its evolutionary mechanisms.