First evidence of host range expansion in virophages and its potential impact on giant viruses and host cells

Virophages are satellite-like double stranded DNA viruses whose replication requires the presence of two biological entities, a giant virus and a protist. In this report, we present the first evidence of host range expansion in a virophage. We demonstrated that the Guarani virophage was able to spontaneously expand its viral host range to replicate with two novel giant viruses that were previously nonpermissive to this virophage. We were able to characterize a potential genetic determinant of this cross-species infection. We then highlighted the relevant impact of this host adaptation on giant viruses and protists by demonstrating that coinfection with the mutant virophage abolishes giant virus production and rescues the host cell population from lysis. The results of our study help to elucidate the parasitic lifestyle of virophages and their interactions with giant viruses and protists.