Viral Lifeforms

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Viruses: They're alive, and they can infect each other


http://www.sciam.com/media/inline/blog/Image/virus.jpgViruses are world champion parasites—think of all the trouble they give us, from Ebola (http://www.sciam.com/article.cfm?id=scientists-uncover-deadly) to HIV. Now French researchers have discovered a viral first … a virus that infects another virus.

A virus that scientists are calling Sputnik was found in a newly discovered strain of so-called mimivirus, which is the world's largest known virus (http://www.sciam.com/article.cfm?id=experts-where-did-viruses-come-fr). Virologist Jean-Michel Claverie (http://www.igs.cnrs-mrs.fr/SpipInternet/article.php3?id_article=39&lang=en), of France's National Center for Scientific Research and a team from the University of the Mediterranean in Marseille, happened upon the strain of mimivirus (http://www.the-scientist.com/blog/display/54915/) swimming in the water of a Parisian cooling tower. When they peeked inside the viral particle, they discovered Sputnik, which consists of only 21 genes.

They found that mimiviruses infected with Sputnik are less effective at infecting amoebae, which is what they normally do.

The researchers believe that Sputnik is the first of a yet-to-be-discovered family of viruses that they suspect may plague large viruses that attack ocean plankton. The French team reported their findings (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature07218.html) in the new issue of Nature, out yesterday.

The finding may answer a long-standing debate posed upon a 2004 cover of Scientific American: Are viruses alive (http://www.sciam.com/article.cfm?id=are-viruses-alive-2004)?

It’s a seemingly simple question, but actually not: On the one hand, viruses can copy themselves and affect the health and behavior of other organisms. But, they require the machinery of other organisms to do any of that.

But, according to Claverie, if mimivirus can both pirate another organism's DNA-copying machinery and fall prey to another virus that does the same to it, then mimivirus is most certainly alive.

"There’s no doubt this is a living organism," he told Nature News (http://www.nature.com/news/2008/080806/full/454677a.html). "The fact that it can get sick makes it more alive."
(Photo: iStockphoto/Henrik Jonsson)

http://www.sciam.com/blog/60-second-science/post.cfm?id=viruses-theyre-alive-and-they-can-i-2008-08-08

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Looking for LUCA

LUCA, the last universal common ancestor, was a single cell that lived perhaps 3 or 4 billion years ago, and from which all life has since evolved. But efforts to reconstruct LUCA's genes by building family trees from modern gene sequences have met with little real success, and basic questions about LUCA's nature remain unanswered. A new theory may help to explain why LUCA has been so hard to find. Perhaps it wasn't a unique organism at all. Instead of some 'blob', perhaps we should think of LUCA as a pool of genes shared among a host of primitive organisms.

http://www.nature.com/nature/links/040219/040219-2.html

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See highlighted text below. Is this evidence of advanced terrestrial life that existed prior to our genetic line?

Call it the ultimate search in genealogy - the hunt for a lifeform that existed more than 3bn years ago and is the common ancestor of everything alive today. The scientists on this search might not agree what the organism might be, but they already have a name: Luca (Last Universal Common Ancestor). Evolutionary biologists who believe that Luca did exist argue that everything from bacteria to birch trees to blue whales is descended from this one living thing.

It's a controversial topic. Not least because some scientists suggest that, if Luca existed, the evolutionary processes at work on primordial Earth might have been quite different to the Darwinian model of natural selection. That's scientific heresy, but it is not stopping the search. At the National Centre for Biotechnology Information in Maryland, for example, a team led by the evolutionary biologist Eugene Koonin is trying to identify Luca's genes. So far they have 600 possibles. Once they can pare it down to the bare minimum, they hope to assemble Luca's genome in the lab.

Despite its differences from Darwinism, Luca is descended from Darwin's theory of evolution by natural selection. Darwin proposed that similar species must have had common ancestors. Each species belonged to a huge family tree but even Darwin was unable to work out whether those trees were connected.

After Watson and Crick's discovery of the structure of DNA and the subsequent birth of molecular biology, scientists began to unpick the differences between different species. But as well as differences, they found similarities - the common molecules of life such as DNA, amino acids and proteins - that suggested differing forms of life were more closely linked than even Darwin had thought. But the latest research on Luca suggests another scientific heresy, this time concerning DNA. It has long been thought that Luca existed when genes were made from DNA's less sophisticated cousin, RNA. But some scientists now believe Luca was DNA-based, suggesting DNA evolved twice.

So what was Luca? The answer depends on which of the three branches of life on Earth is shown to be the oldest - bacteria, archaea (single-celled organisms such as the extremophiles, which can endure incredibly high temperatures and pressures) and prokaryotes (everything else, including all plants, animals and fungi). The answers could be decades or even centuries away but there's no real rush among scientists. Luca has been waiting to be discovered for some time already.


http://www.guardian.co.uk/science/2005/oct/10/g2