Sputnik takes on the mamavirus

A French team of virologists has discovered a new strain of giant virus with something interesting attached - a tiny virus that seems to infect its viral host.

The team, lead by Didier Raoult from France's Centre National de la Recherche Scientifique, and colleagues were looking at a new strain of Acanthamoeba polyphaga mimivirus (APMV), which they had discovered infecting amoeba found in a UK cooling tower in 2003.

Mimivirus is massive - it is larger than some bacteria and is visible under an optical microscope - as isthe new strain the team found, this time in a cooling tower in Paris. They have named it mamavirus, as it is even bigger than mimivirus.

Even more interesting is what is attached to mamavirus - a tiny virus that seems to have hijacked the virus factory created in amoebae by the mamavirus and started to replicate.

The team has nicknamed this virus Sputnik and believes it could be considered a 'virophage', as it infects and sickens its virus host much as bacteriophages infect and sicken bacteria.

They also believe it could be a vehicle that mediates lateral gene transfer between giant viruses. Sputnik's genome contains three genes thought to be acquired from mimi and mamavirus, as well as an integrase gene that seems to have come from archaeal viruses.

The virophage as a unique parasite of the giant mimivirus was published in advance online in Nature [doi:10.1038/nature07218] and an accompanying news article appears in today's printed edition.