Ocean trawl reveals huge virus that infects amoebas

Posted on 11 Oct 2011


Mimivirus (top) and Megavirus (bottom). Scalebar = 200 nanometresThe largest virus yet discovered has been isolated from ocean water pulled up off the coast of Chile.

Called Megavirus chilensis, it is 10 to 20 times longer than the average virus.

It just beats the previous record holder, Mimivirus, which was found in a water cooling tower in the UK in 1992.

Scientists tell the journal PNAS that Megavirus probably infects amoebas, single-celled organisms that are floating free in the sea.

The particle measures about 0.7 micrometers (thousandths of a millimetre) in diameter.

“It is bigger than some bacteria,” explained Professor Jean-Michel Claverie, from Aix-Marseille University, Marseille, France.

“You don’t need an electron microscope to see it; you can see it with an ordinary light microscope,” he told BBC News.

Viruses cannot copy themselves; they need to invade a host cell if they want to replicate.

Like Mimivirus, Megavirus has hair-like structures, or fibrils, on the exterior of its shell, or capsid, that probably attract unsuspecting amoebas looking to prey on bacteria displaying similar features.

A study of the giant virus’s DNA shows it to have over a thousand genes, the biochemical instructions it uses to build the systems it requires to replicate once inside its host.

In the lab experiments conducted by Professor Claverie and colleagues, in which they infected fresh-water amoebas, Megavirus was seen to construct large trojan organelles – the “cells within cells” that would produce new viruses to infect other amoebas.

via BBC News – Ocean trawl reveals ‘megavirus’.

Posted in: Biology