French scientists using the Genome Sequencer System from 454 Life Sciences have identified a small virus that can actually be parasitic to a larger one.
The 50nm virus, named Sputnik, is associated with a new strain of the giant Acanthamoeba polyphaga mimivirus (APMV) and is believed to represent a currently unknown family of viruses.
The study, entitled 'The Virophage as a Unique Parasite of the Giant Mimivirus', appeared in the 4 September issue of Nature.
The relationship between Sputnik and the mimivirus appears to be beneficial for Sputnik's viral reproduction.
On its own, Sputnik does not replicate very well in amoeba cells.
However, when the amoeba is also infected with the mimivirus, Sputnik thrives and multiplies in the viral factory created by the mimivirus.
Due to the parallels in its lifecycle with bacteriophages, the virus was classified as a 'virophage'.
The Sputnik genome, as determined by shotgun 454 Sequencing, is an 18-kilobase circular double-stranded DNA and contains genes that are linked to viruses infecting each of the three domains of life: Eukarya, Archaea and Bacteria.
Therefore, the virophage could be a vehicle mediating lateral gene transfer between giant viruses.
The discovery sheds light onto the interactions between viruses and has implications on the evolution of these infectious agents, as is evident from the gene mixing and matching within the virophage.
