Talk:Mimivirus

Life debate

xyz1323: How can a "Mimivirus" live? It's a living organism, like any other virii. Did you sleep through biology class or something? -Alex 12.220.157.93 06:43, 26 December 2005 (UTC)

It's my understanding (from a strictly layman perspective) that there is still some debate as to whether viruses are living entities or merely shards of living entities, and not themselves alive. It depends on how you define "living organism." A common definition is that an organism is "a living thing that has (or can develop) the ability to act or function independently." The key word is "independently"; most viruses cannot perform these functions without preying on a cell. The mimivirus blurs the distinction between a virus and a bacterium (for example by sythesizing proteins), so some consider the mimivirus to be a life form even if they consider simpler viruses to be nonliving.

I'm more interested in the theory that an ancestor of the mimivirus (or a similar large DNA virus) was also an ancestor of the cell nucleus. This would mean that at least two organelles in each (eucaryotic) cell were once seperate entities (most believe that mitochondria and chloroplasts evolved from purple bacteria), which implies that the eucaryotic cell is actually a cell colony. Endosymbiotic theory thus implies that many "single-celled" organisms actually aren't! archola 00:48, 9 February 2006 (UTC)

JustInterested: If it is alive, but the basic definition of a virus determines that it is a nonliving thing, will the researchers be more likely to clasify it as a bacteria, or keep its classification as a virus, but change the virus definition? I saw that it was included on a tree of life found on this website.However, it was seemingly closer to being a eukaryotic cell than an archa- or eu- bacterial one. What do you think of this? And Alex, start paying attention in Biology class-- No viruses before this one have had a real potential to be considered alive. <also from a layman perspective.. if there was one that came as close as Mimi, I have not heard of it.> — Preceding unsigned comment added by 66.162.225.66 (talk • contribs)

Actually both of you are right (or wrong). Before, there was a long and seemingly never ending debate on whether viruses were living entities or not. Now though, we have evidence that at least some of them could be classified as alive. I'll have to read more about it since I just learned of it from Slashdot (cringe) which is really shameful considering I'm an ardent reader of Science. - 127.* 15:59, 1 March 2006 (UTC)

And then of course, there is the debate over whether or not (some?) viruses form a fourth domain of life. Grigory Deepdelver AKA Arch O. La^TalkTCF 22:56, 23 March 2006 (UTC)

JustInterested: Alright, I'll change my statement-- the majority of viruses have not recently been given the chance to be considered alive, until mimivirus. Is this the actual fact, or is it something that I just seem to be making up? — Preceding unsigned comment added by 66.162.225.66 (talk • contribs)

Act or live independently? Not necessary, some life form does live only by depending on others. They are called parasites ---- pls pay attention in biology class. — Preceding unsigned comment added by 202.156.6.54 (talk • contribs)

Yup, they could be parasites that lost the ability to live independently. That's yet another hypothesis. Grigory Deepdelver AKA Arch O. La^TalkTCF 22:56, 23 March 2006 (UTC)

Nothing can live "independently". You'd die if you were dumped in a vacuum (and you wouldn't reproduce there, either). Even those autotrophs which can live completely without relying on other organisms (note: this group in particular already excludes all members of the animal kingdom... even though the word "animal" literally means "something which is alive") still need particular materials from the Earth's ground and atmosphere, and in some cases sunlight. For a species to live, it must have a suitable environment containing certain necessary features - and for virusses, one of these features just happens to be the presence of cellular life forms. -- Milo

Update

I think this page needs updating and some clarification of the "facts". From reading around the current given number of genes for Mimi is 911 (protein coding); with some news-sites quoting ~900, which is possibly where the original value came from at the top of the article. The common value given for number of base pairs is ~1.2Mbp 1,200,000 not 800,000. The language used in the wiki article suggests “bases” not base pairs; since the virus has double stranded DNA this is a little confusing?!
It might be nice to include a few speculative Mimi topics: the possibility of human infection, evolved to look like tasty bacteria to get amoeba actively hunting it...
http://www.virologyj.com/content/2/1/62
The NewScientist mag has recently written an article about Mimi, so its likely there will be more traffic to this page. It would be great if it wasn't just a bunch of links to sources. This article hasn't developed much since I came here a few months ago! I guess I could add some stuff if no one else is bothered :S ~~Matt Oates 21:34, 25 March 2006 (GMT)

JstInterested: This page obviously needs updating-- and somone willing to clean it up and update it. If somone is interested, I'm sure no one will stop them.

Oh I'll be flexing my little keyboard muscles here soon enough, don't you worry -- Serephine ♠ talk - 12:40, 16 June 2006 (UTC)

Update complete! -- Serephine ♠ talk - 19:37, 7 July 2006 (UTC)

Whoa! Just came back to this page since I noticed a minor edit on my watch-list! Nice job Serephine, thanks :] I've nominated the article for GA status. MattOates (Ulti) 12:30, 3 March 2007 (UTC)

On second thought from looking at the history thanks to all the people who edited :] since it's quite a few! —The preceding unsigned comment was added by MattOates (talk • contribs) 12:33, 3 March 2007 (UTC).

Which came first?

The article states:

Because its lineage is very old and could have emerged prior to cellular organisms, mimivirus[...]

Since virusses rely on cellular organisms for reproduction, and this trait seems to be integral to what a virus is, how could any virus possibly have existed before cellular organisms came around? -- Milo

Unless I'm mistaken, aren't there some viruses capable of self-assembly?

To allow myself the luxury of speculation, perhaps after billions of years of evolution, obligate parasitism simply works better for the majority of viruses. Indeed, considering mimivirus itself was originally mistaken for a bacterium, maybe there are viruses out there that we simply don't know about, because we haven't looked for them... --Xanthine 17:52, 6 December 2006 (UTC)

The problem, however, is that the viral capsule is inherantly incapable of division: it has to be built from the outside, therefore absolutely necessitating a host that can express the viral proteins. In short, a solid virus, even if it had a metabolism, cannot make another virus. The whole idea, therefore, of "self assembly" is meaningless, because one virus cannot come from another. It is far, far more likely that viruses are the descendents of cellular processes. The whole section we have devoted to this idea is almost entirely speculation. Can somebody add some citations to it? – ClockworkSoul 06:08, 7 December 2006 (UTC)

Valid points. All in all, it's an interesting topic for discussion. A friend of mine is a doctor, and I know he has some papers on Mimivirus. I'll see if I can get him to take a look at this page... --Xanthine 13:37, 11 December 2006 (UTC)

But where do cellular processes come from?

Viruses have much simpler structure than cells. Viroids (RNA molecule with just 240 to 600 nucleotides or 10,000 atoms)have even simpler structures. Hence it seems reasonable that viruses and viroids were the first to emerge in evolution. At that time, there would be no cells, and these "creatures" would be just replicating using the available enzyme molecules in the primordial soup. Today, viruses can also be replicated biochemically without cells. Leslie Orgel conducted experiments where RNA nucleotides join to produce RNA, which later self-replicate. Spieglemen used protein enzymes Q-beta replicase to help Q-beta viral RNA replicate in test tubes and artificially selects virus RNAs to drive chemical evolution. DNA can be replicated using polymerase chain reaction (PCR). I hold the gene-centric rather than cell-centric view of life where cells are not necessary. The mimivirus you mentioned could well be a missing link of the evolution from viruses to cells, and not the other way round. It is easy to say that viruses are just "drop-outs" from cells, but it is important to ask: Where does the complex cellular structures with all its myriads of organelles like nucleus, ribosomes etc come from? As far as we know, the early days of earth was so hot that cellular structures couldn't have existed.

The phospholipid bilayer making up a large part of the cell membrane is an emergent structure in the presence of water, it isn't a bad assumption to make that this then encapsulated early self replicating chemical processes forming simple cells. Can the same be said for viruses that are made from proteins? Plus who says it was too hot? Hyperthermophiles exist on Earth today at high temperatures Strain_121 at the very surface (top centimeter) of a hot ocean where there is also light its cooler since the water is evaporating and heat radiates into the atmosphere. The myriad of organelles aren't required in all cellular life, bacteria for example. Symbiogenesis can explain how simple cells can come together to form more complicated cell-organelle relationships leading to the formation of modern eukaryotic cells over time. MattOates (Ulti) 23:34, 14 March 2007 (UTC)