Hints of Life's Start Found In a Giant Virus 158
An anonymous reader points out this update on the world's largest virus, discovered in March. Chantal Abergel and Jean-Michel Claverie were used to finding strange viruses. The married virologists at Aix-Marseille University had made a career of it. But pithovirus, which they discovered in 2013 in a sample of Siberian dirt that had been frozen for more than 30,000 years, was more bizarre than the pair had ever imagined a virus could be. In the world of microbes, viruses are small — notoriously small. Pithovirus is not. The largest virus ever discovered, pithovirus is more massive than even some bacteria. Most viruses copy themselves by hijacking their host's molecular machinery. But pithovirus is much more independent, possessing some replication machinery of its own. Pithovirus's relatively large number of genes also differentiated it from other viruses, which are often genetically simple — the smallest have a mere four genes. Pithovirus has around 500 genes, and some are used for complex tasks such as making proteins and repairing and replicating DNA. "It was so different from what we were taught about viruses," Abergel said. The stunning find, first revealed in March, isn't just expanding scientists' notions of what a virus can be. It is reframing the debate over the origins of life."
Re:What is life? What is a virus? (Score:5, Informative)
It can't reproduce entirely on it's own, so it's not 'free living'. It does need a host. It's just it doesn't need the host for some of the tasks that most viruses need the host for.
It would seem that, instead of being a primitive form that was at the base of the the genetic tree, it's more likely to be an offshoot. It hijacked some additional molecular machinery from an extant organism rather that figuring it out on it's own.
Re:What is life? What is a virus? (Score:5, Informative)
There are many differences between viruses and prokaryotes, but the main thing that seperates them from life is that they don't have ribosomes (https://en.wikipedia.org/wiki/Ribosome). Ribosomes are necessary for the production of proteins and no known virus encodes thier own ribosomes (they use the ones from their host cell). Some viruses, such as the one mentioned in the link, do encode genes to make some tRNA (needed for translating the genetic code into protein).
Re:What is life? What is a virus? (Score:5, Informative)
Oh, now I went ahead and read TFA. It's all complicated and confusing.
The current thinking is indeed that viruses are an offshoot of 'modern' life (modern being sometime after the archea). These critters, because they contain gene sequences that seem to predate the prokaryote - eukaryote split and because we know that bacteria just love to transfer genetic information 'horizontally' - that is by tossing bits of DNA and RNA around so some unrelated organism can incorporate it into their genetic apparatus as opposed to simply eating it - that it may be that these big viruses started sometime after the RNA hypothesis took hold and created the first self replicating organisms. Or at least helped those first 'organisms' diverge and multiply.
At least it's a testable hypothesis. Once you have sequenced a number of the big virus genes and compare them you would presumably get an idea how old they are.
It would seem that even if this mechanism held, the critters would have had a long time to morph into another ecological niche so it would be hard to pin down what their function was (if any) at the beginning of life. But perhaps the Central Dogma is barking up the wrong tree after all.
Re:What is life? What is a virus? (Score:5, Informative)
Uh, they most certainly have extremely crisp boundaries. Species are classified by the ability of two organisms to breed with one another.
The "Species problem" [wikipedia.org] shows this not to be the case. The specific issue you mention is in the introduction:
"Another common problem is how to define reproductive isolation, because some separately evolving groups may continue to interbreed to some extent, and it can be a difficult matter to discover whether this hybridization [wikipedia.org] affects the long-term genetic make-up of the groups."
That being said, I was taught the same way as you and only learned differently when I started teaching it myself. Now when I explain classification, I try to intersperse phrases like "usually classified as..." or "One good way to classify it is...". I usually try to reinforce that there are many ways to classify, show them the most common way(s), and encourage them to make their own classifications if those ways fail. This is especially prevalent in biology where phylogenetics [wikipedia.org] (usually based on RNA, dividing groups into clades) is currently intermixing with more traditional taxonomy [wikipedia.org] (usually based on morphological traits, dividing groups into Linnaean classification)[1] [wikipedia.org].
Re:Yet another proof creation doesn't work! (Score:5, Informative)
Re:Well (Score:5, Informative)
I, for one, welcome our new virii overl...oh forget it, this meme is no longer funny.
Virii? Nitpicking, I know, but that particular abuse of the language makes me cringe, it really does, because it is so bizarrely and emphatically wrong on far too many levels.
Even if 'virus' had been the singular form of a latin word, the plural would not have been 'virii', with double 'i' at the end. 'Viri', possibly, but 'virii' would have to come from 'Virius', a personal name - check out:
http://en.wikipedia.org/wiki/L... [wikipedia.org]
and
http://en.wikipedia.org/wiki/V... [wikipedia.org]
Finally, from http://en.wikipedia.org/wiki/V... [wikipedia.org]:
Etymology
The word is from the Latin virus referring to poison and other noxious substances, first used in English in 1392.[10] Virulent, from Latin virulentus (poisonous), dates to 1400.[11] A meaning of "agent that causes infectious disease" is first recorded in 1728,[10] before the discovery of viruses by Dmitri Ivanovsky in 1892. The English plural is viruses, whereas the Latin word is a mass noun, which has no classically attested plural. The adjective viral dates to 1948.[12] The term virion (plural virions), which dates from 1959,[13] is also used to refer to a single, stable infective viral particle that is released from the cell and is fully capable of infecting other cells of the same type.[14]
IMO, since 'virus' is a modernism - an old word used in a completely new way - it is reasonable to treat it grammatically as a modern word: one virus, multiple viruses, just like 'one bus, several buses' ('bus' from 'omnibus', but let's not go there). Apart from that, you would use a a nominative singular here: '... our virus overlords ...'
Re:Well (Score:2, Informative)
Mod parent up, he is spot on. The english plural is viruses and that's it.
The word virus has no attested plural form in latin. One could argue that if the word had a plural form, it would be "vira", though, since it's neutral.
http://linuxmafia.com/~rick/fa... [linuxmafia.com]