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

Yes. The current human definition of "life" is nomothetic. Along the way it has been influenced by cell theory, etc. Facts are that until sentients discover any life that is not a collector and conduit, of/from a material or an energy source, all life must be considered somehow dependent.

Even "non-living" minerals come as elements created by stellar processes, and interactions dependent on the presence of other substances, even of the same general kind.

To advance the discussion, would suggest defining life more simply until a better way can be found:

How about that organisms are matter that can reproduce similar forms, transform over generations/evolve, are based on (or are themselves bits of) a code (DNA/RNA, etc.) and affect their environment whatever that is.

That might suffice at least until some beings manifest that do not fit this formulation. -- Ala Balsam Collestan — Preceding unsigned comment added by 74.124.165.189 (talk) 23:50, 15 January 2020 (UTC)

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)

Im a Microbiology student about to graduate, currently studying virology. From my understanding, there is a lot of debate within the scientific community about early primordial evolution of life from simple molecules and viruses are showing more and more prominence in the current theorys. Geneticly, Mimivirus diverged earlier than eukaryotic cells, because of its gene content and how that relates to euykaryotic genes. However, what we think of as a cell was thought to be very different at this primordial point, more like membrane bags that viruses popped in and out of while shuffling around their genes with each other. It is from this that different viruses emerged and then when cells as we know them emerged, the viruses modified themselves to infect them. Its much, much more complicated than that and there are a bunch of conflicting and interfering ideas on the subject. suffice to say that it was all a bit of a mess back then and what the sentence "Because its lineage is very old and could have emerged prior to cellular organisms" means is that the genetic content diverged largely as it is seen today earlier than the cellular lifeforms that we see today. It's complicated I know, heres an article that serves as a good starting point for the topic: -Evolution of complexity in the viral world: the dawn of a new vision. Koonin EV, Dolja VV. Virus Research volume 117 issue 1 page 1-4 Feb 2006-

Hope this helps, Numzana 23:28, 14 October 2007 (UTC)

Hmm... From what I've read, there's a number of theories revolving around Mimivirus. On of which, as Numzana mentioned, is that viruses diverged from prokaryotes shortly before the evolution of eukaryotes and evolved to lose their ribosomes and parasitize other organisms. Another theory maintains that Mimivirus is an anomaly created through horizontal gene transfer between a normal virus, its amoeba host, parasitic prokaryotes within the amoeba, and the "Sputnik" virophage and that the theory of viruses diverging from prokaryotes is utter poppycock. As to which, if any, theory is true, no-one knows as of yet. 173.180.72.42 (talk) 22:34, 5 December 2010 (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)

These early self-replicating processes are the viruses. They later got encapsulated by the bilipd layer to form cells. Hence viruses appear before cells.

Small self-replicating bits of nucleic acid are a simple and essential intermediate in the origin of life, but calling them "viruses" is a stretch. The distinction is that so far as I know, every modern virus known to man is a) incapable of making protein and b) requires protein to function. This is no small distinction, because the entire elaborate structure of the ribosome and its associated factors and metabolic machinery are required for usual methods of protein synthesis. (There are some clever alternatives used for making antibiotics - see Nonribosomal peptide - but I'm not aware of any virus making a capsid, etc. using such tricks) I cannot swear to you that no primordial snippet of catalytic RNA could have survived from the beginning of the world until this day without ever having been part of a normal cycle of cell replication, but if it did, it has somewhere along the line developed a great need for ribosomes it doesn't have, and has borrowed enough sequences from ribosome-containing cells to make all the protein-coding genes we identify in it today.

Of course, you could postulate that self-replicating RNAs developed protein synthesis before the proper cell membrane, and then some never became part of cells. The problem is that it is hard to picture a complete protein biochemistry, at least one of the usual ribosome-oriented type with loose aminoacyl-tRNAs and the wizard's stew of biochemical precursors to amino acids, existing free or within a typical tight-packed viral capsid. One would think that the such a protein synthesis machinery open to the environment would have special adaptations to keep components from escaping, and probably would have use some more rudimentary genetic code than the completed cell. Yet none of these primitive features show up in viruses either.

The bottom line is that viruses by their nature could have picked up snippets of code anywhere, but they are not primordial organisms from the first days of life. Wnt (talk) 15:32, 8 August 2008 (UTC)

GA feedback

I'd like to see the "notes" and "references" sections combined, so that they are all in-lined references. Otherwise I think it looks Good. Pete.Hurd 19:01, 17 March 2007 (UTC)

I'd like references for statements in the lead section, add links to "pneumonia", the reference "(M. Suzan-Monti, 2006)" at the end of the first paragraph of the "Replication" section should be in-lined. I think the section "Implications for life" could have a better title, maybe including the phrase --definition of "life"-- but I can't come up with one that I'm happy with... Pete.Hurd 19:38, 17 March 2007 (UTC)

I've dealt with the referencing and renamed the sections. Lead sections don't usually need refs as they should summarise the rest of the article. TimVickers 21:07, 26 March 2007 (UTC)

Are there four other NCLDV families, or five?

The article says "nucleocytoplasmic large DNA viruses (NCLDV), which includes four other families: Poxviridae, Iridoviridae, Phycodnaviridae, Asfarviridae and Coccolithoviridae." That is five families, not four. I tried to look this up and found Coccolithovirus listed as a genus under family Phycodnaviridae, but here on wikipedia Coccolithoviridae is a family.

Could someone who knows this field check this and either change "four" to "five", or trim the list, or reword things to remove the word "four", or something? Thanks. Atomota 04:29, 13 October 2007 (UTC)

Iv looked it up, coccolithoviridae should be removed, im new to wikipedia though and dont know how to change the article. can someone change this part? Numzana 23:45, 14 October 2007 (UTC)

Genome Linear or Circular

From my review of the literature, the genome is indeed Linear but has 900 base pair inverted repeats at each end which would enable it to become circular within a cell. I think this should be mentioned in the Genome section as few viruses in this group really have a linear genome when inside a cell.

thoughts, comments? Numzana 00:16, 15 October 2007 (UTC)

Evolutionary path

The speculation about this virus as an "intermediate" or even a precursor to life depends on the idea that this virus represents some stripped-down or prototype version of a bacterium or the like. However, you could draw multiple scenarios of the evolution:

1. A free-living organism evolves into an obligate intracellular parasite, then develops a hard viral capsule to protect it.
2. A tiny virus begins to acquire additional genes for some reason and gets larger and larger. (This would hint that there is something unusual about amoeba metabolism that encourages viruses to bring their own toolkit)
3. (implied in some discussion above) The virus somehow developed as a primordial free-living organism and is less degraded from that original free state than most

By intuition I favor the second model, but the point is, you don't know where you are until you know where you came from. Existing evidence is: [1] Mimiviruses have a special promoter for their own genes, which supposedly makes them something ancient and unique - but promoter sequences are easy to evolve and the virus has a strong pecuniary interest in keeping its resources private. [2] I haven't accessed this, but I infer from the search blurb that the viruses fall out in their own family somewhere among the eukaryotes. Deep taxonomy often includes publications of believable-looking trees that are later disputed, but if it really did come from eukaryotic sequence - perhaps its host organism - then it is not some tiny primitive bacterium-like thing.

The bottom line is that any speculation about the nature of this organism should be subordinate to sourced information about its evolution. Wnt (talk) 14:58, 8 August 2008 (UTC)

mamavirus

No longer the largest known virus?

An article on Discovery News states that a larger virus has been discovered and dubbed 'mamavirus'. I can't find much on it but can anyone confirm this from a good source? Rob.desbois (talk) 08:15, 14 August 2008 (UTC)

yea mamavirus is larger. A good source —Preceding unsigned comment added by 82.122.203.62 (talk) 17:32, 20 September 2008 (UTC)

I've added a brief mention. Is the mamavirus a kind of mimivirus, or are they a distinctly different kind of virus? --68.0.124.33 (talk) 15:16, 18 July 2009 (UTC)

The intro should now be corrected as the mimivirus is no longer the largest virus. —Preceding unsigned comment added by 206.167.194.114 (talk) 21:06, 18 April 2010 (UTC)

According to researchers, Mamavirus is a second, larger strain of APMV, so yes, it is a type of Mimivirus. Seeing as the Mamavirus page barely contains any information, I suggest that the Mamavirus page be merged into the Mimivirus page. 173.180.72.42 (talk) 22:26, 5 December 2010 (UTC)

According to the new version of the page with megavirus as new biggest virus shouldn't it be now third biggest one? also under genome-part it is still mentioned as biggest one. — Preceding unsigned comment added by 81.172.94.30 (talk) 11:16, 6 February 2012 (UTC)

mimivirus has its own virus?

Sorry if I am not going about this the right way but I have heard (and read) that a very small virus has been found associated with mimivirus. I was wondering if anyone else thought that this would be a pertinent addition to the article? Again sorry if I am miss-using the talk page source: Bernard La Scola et al (2008) Nature, 455, 100-104

That would definitely be a pertinent addition to the article. Evenfiel (talk) 16:21, 23 February 2009 (UTC)

I've added a brief mention of that smaller virus. But I am a bit confused about what kinds of viruses it infects. Does it only infect the mamavirus, or does it also infect the previously-discovered mimivirus? --68.0.124.33 (talk) 15:16, 18 July 2009 (UTC)

It infects both interchangably. 173.180.72.42 (talk) 22:27, 5 December 2010 (UTC)

Of interest from American Scientist

Of interest from July-August 2011, Volume 99, Number 4, page: 304, DOI: 10.1511/2011.91.304 American Scientist: Giant Viruses: The recent discovery of really, really big viruses is changing views about the nature of viruses and the history of life by James L. Van Etten? It contains a Bibliography, and is the Feature Article cover story. 99.181.142.15 (talk) 04:42, 2 July 2011 (UTC)

Self-contradiction (or unclear)

The section on Implications for defining "life" contains this sentence: ~Some genes unique to Mimivirus, including those coding for the capsid, have been conserved in a variety of viruses which infect organisms from all domains." This seems self-contradictory: if the genes are unique to Mimivirus, that means they aren't found in anything else, right? Then how can they have been conserved in a variety of other viruses? Steorra (talk) 19:01, 19 July 2013 (UTC)

virophage immunity

This is interesting:

http://www.nature.com/news/crispr-like-immune-system-discovered-in-giant-virus-1.19462

Maybe someone could add a summary to the article. I don't have the knowledge to do this properly myself. 173.228.123.101 (talk) 01:20, 1 March 2016 (UTC)

Yes, it is notable. Thanks. BatteryIncluded (talk) 01:38, 1 March 2016 (UTC)

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Source for list of species in infobox

Does anyone know where this comes from? The ICTV page I've seen [3] seems to state only Megavirus chilensis but might be out of date. (I find their webpages hard to navigate.) Espresso Addict (talk) 05:18, 3 February 2020 (UTC)