“What we find is that inside the amoeba, a virus can meet bacteria, archaea and prokaryotes. A whole new repertoire of an organism can be composed,” said Didier Raoult, a microbiologist at the University of the Mediterranean in Marseille, France. [..] This string of discoveries — and there are many more that the researchers have yet to describe in formal literature — shows that giant viruses are not an oddity, but a domain of the organismal kingdom that scientists are just starting to explore. And all the giant viruses have been found inside amoebas, a group of single-celled animals so common that it’s easy to overlook its uniqueness. The largest genome in the world, for example, belongs to an amoeba. “It’s 200 times bigger than the human genome,” said Raoult. [..] “It’s a whole world in there,” said Raoult.
According to Raoult, the amoeba melting pots likely had analogues billions of years ago, when eukaryotes — complex cells, with a nucleus and other sophisticated machinery — had yet to evolve. How they evolved is a scientific mystery, but Raoult thinks that prokaryotic forerunners of modern amoebas may have provided the necessary incubators for eukaryotic evolution. Whether this actually happened may never be known, but Raoult added that it’s definitely continuing today. “We have this idea that everything is derived from something with very old roots. But there is still creativity going on, creating new origins,” he said.
(via http://www.wired.com/wiredscience/2009/12/giant-viruses/)