The virophage as a unique parasite of the giant mimivirus

We just read an article from Nature by Scola et al. Viruses have always presented a problem to scientists. Are they alive? I was taught back in middle school, that no they are not, but that they are that gray area between the black and white. Biologists generally define a living organism as having the ability to grow, adapt, respond to stimuli, reproduce, maintain homeostasis, metabolize, and have an organized structure. Viruses tend to meet most of the requirements but can't reproduce by themselves without a host. So most biologists don't consider them to really be alive.

The authors of this paper have discovered a virus, they named it Sputnik, that will attack other viruses. They have termed it a virophage. The virus it was attacking was the Acanthamoaeba polyphaga mimivirus, the largest known virus. The combination of the two viruses, they referred to as a mamavirus (originally they thought this was a new virus). The mamavirus was found within an amoeba. Sputnik then proceeded to rapidly grow inside the amoeba, within the viral factory. The growth of Sputnik appeared harmful to the mimivirus. The presence of Sputnik cause abnormal mimiviruses with thicker capsid layers, sometimes accumulating at one side of the mimivirus.

Sputnik appeared to decrease the amount of mimivirus growth and the killing of the amoeba. This appears to the authors as a virus (the mimirirus) that is “sick” (infected with Sputnik). This leads to questions like, if a virus can get “sick” then does this mean that it is alive? Can something get sick if it cannot reproduce by itself (and is thus not alive)? Do we now have to change our definition of living?

Another interesting thing that they have found, is that Sputnik contains genes that appear to be linked to viruses that can affect all domains of life. This leads us to conclusions that Sputnik is derived from an ancestral organism from back before the domains separated into their three catagories.

I was mostly confused while reading this paper as to the distinction between mamivirus, mimivirus, and all of the other organisms that had homologues of genes found within Sputnik. Looking back over the paper, the mamavirus appears to be related to the mimivirus, they are not the same thing.

It would be interesting to see what the effects of this paper and organism will have on science. I wonder if this will revolutionize virology (at least) and possibly the rest of biology.