July 19, 2013
World’s Largest Virus Discovered By French Researchers
Brett Smith for redOrbit.com - Your Universe Online
Once thought to be tiny and containing only a handful of genes, viruses have been redefined over the past decade by the discoveries of specimens the size of bacteria that contain 1,000 genes or more.
According to a newly published report in the journal Science, French researchers have discovered a virus 1,000 times larger than the flu virus and which has almost 2,600 genes - the biggest virus known to date.
Dubbed "pandoravirus," the study authors said only 6 percent of the massive virus' genes actually have a known function. The rest remain a mystery for the moment.
"We believe we're opening a Pandora's box - not so much for humanity but for dogma about viruses," study co-author Jean-Michel Claverie, an evolutionary biologist at Aix-Marseille University in France, told the New York Times. "We believe we're touching an alternative tree of life."
In 2011, Claverie and his colleague Chantal Abergel found something in a water sample collected off the coast of Chile that appeared to be infecting and killing amoebae. Appearing too large under the microscope to be a conventional virus, the researchers simply dubbed it NLF - or new life form.
After finding something similar in an Australian lake 10,000 miles away, the researchers released a report stating that they had found the largest viruses to date, which they called Megavirus chilensis.
The team's latest discovery, Pandoravirus salinus, came from the same Chilean water sample as M. chilensis, and does not make its own proteins or reproduce by cellular division. According to the study authors, pandoraviruses exhibit a typical viral life cycle - invading an amoeba host, taking over its nuclei, producing hundreds of new viral elements and eventually rupturing the cell from within.
Claverie said giant viruses probably branched off from other microbes several billion years ago.
"The type of cells they may have evolved from may have disappeared," he said, adding that viral giants like pandoravirus, may "not be rare at all."
These viruses may be so common that we could even be hosting them in our own bodies, say the researchers. A study published on July 2 revealed the discovery of a giant virus in blood taken from a healthy donor. That study also showed evidence of giant virus antibodies in four other individuals.
So far, scientists have said that these massive viruses only infect single-celled organisms, and any living inside us could only be attacking the microorganisms that we also host.
"I don't believe we have the proof at the moment that these viruses could infect humans," Claverie said, before adding, then again "never say never."
Our understanding of viruses has come a long way since the 1930s, when newly developed microscopes allowed scientists to visualize them for the first time. Watching the tiny viruses invade cells and use them to replicate themselves, these twentieth-century scientists helped establish the notion that being small and simple is necessary for the viral life cycle.
The very first giant viruses were discovered in 2003 from samples taken out of cooling tower water. The French team that discovered them came to find that the spherical, oversized viruses contained 979 genes - forever changing the notion of what a virus could and could not be.