Science Questions

Are Pandora viruses a fourth domain of life?

Thu, 1st Aug 2013

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Damon asked:

Scientists have recently discovered the Pandora viruses. It was said they could possibly suggest a fourth domain of life. I was wondering what the implications of these viruses could be and how could we use them?


Chris - Itís amazing. What do you know about it Damon? Tell us what you know adenovirusabout it.

Damon - I donít know much. I think they said you could even see it with a standard microscope. It was that large.

Chris - Yeah. Itís published in Science this week. Itís by a group in France who discovered this. Actually, they discovered this massive virus in a pool of freshwater, a pond basically, near Melbourne in Australia. They also found a very similar virus off the coast of Chile and these viruses, they've dubbed the Pandora viruses because when they had a look at them genetically, then it was anyoneís guess what was in there because they did not bear any resemblance to any kind of life than weíd ever found before.

So, we talk about life having 3 established domains. There's the eukaryotes Ė cells like ours. There's prokaryotes Ė they're bacteria, we know about those and then there's another sort of ancient evolutionary spinoff called the archaea. And we were very happy that all life on earth fitted into those 3. Now, weíve got these viruses that have come along. That a) are huge, they're more than a thousandth of a millimetre across which is in virus terms, that's like you walking down the street and bump into someone 60 feet tall. They are enormous, these viruses and they bear no genetic resemblance to anything else that exists on the earth.

So, the big questions are, why do they exist? Why are they so huge? I mean, what they do is they live on amoebae, these little single-celled organisms, they prey on them. As I said, absolutely enormous with a huge genome. They've got 2.5 million genetic letters in their genome, which is massive. I mean, itís 10 times bigger than your average virus does. So, scientists are saying, 'well, when we look in the sea and we find all these bacteria that we can't grow in culture.' Actually, they might not be bacteria that we can't grow at all. They might be viruses. These massive viruses that we previously hadnít realised because the people who write the paper have said - well actually, 13 years ago looking in the literature, people described these funny particles and they didnít know what they were. They thought they were some funny hard to grow bacterium because they were so big, because they're literally 10 times bigger than a normal virus. And now, they realise they are a virus, but we donít know what the hell they are.

Dave - So, when you say then nothing like anything else say in life basically, so if they're a virus, surely, they must be hijacking another animals sort of replication machinery. So surely, it can't be that different otherwise it wouldnít work.

Chris - Sure, the genetic code is exactly the same, so a gene in them will the same sort of gene, it would work the same way in one of our cells and vice versa. They havenít rewritten the genetic code, but they prey on amoebae and they just make more new viruses and itís interesting because what most viruses do when they make a virus particle is that they make the coat of the virus and then they stuff the genetic material inside. These things start basically almost like they're knitting a jumper. They knit, the coat as well as the genetic material into it all at once. So, they have this really weird way of growing and they have genetic material, they donít use genes which are used by any other organisms that we know of apart from them. So, exactly why they exist and where they've come from, we donít know. They are completely alien species.  Are you spooked, Damon?

Damon - Not so much spooked as just confused.

Ian - I'm just wondering if these are one of the hangovers from the Precambrian when you had a huge diversity of different life forms and some of those went on into the Cambrian and produced really exotic things that then suddenly vanished. Maybe these were something really exotic, but they just happen to have been saved in the deep oceans and places like that of obscure places, and they're part of what went on to be the Burgess Shale type things.

Chris - Now, they've been discovered, I guess weíll look in and weíll find out, but itís very interesting, isnít it? 


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One of the most amazing things I've read this year.
A blue print over life?

"To find out more about the Pandoravirus, the authors sequenced their genomes.

The first thing that was notable was that the genomes were enormous. The larger of the two was 2.8 million bases long, which is larger than the genomes of many parasitic bacteria (for comparison, E. coli's genome is 4.6 million bases). There were over 2,500 potential genes in that sequence, and the startling thing was how many of them were new to biologists. Only 15 percent of them lined up to known sequences, and half of those just had a small structural similarity in the middle of a larger gene. Eliminating those meant that just seven percent of the genes matched anything in our databases. Only 17 genes matched sequences found in Megaviruses, and under five percent looked like they were stolen from the host amoeba. The virus was clearly something entirely new." yor_on, Fri, 27th Dec 2013

One may state the uniqueness of the Pandoravirus.  And, it will be interesting to see what proteins are encoded for, and what the thousands of genes do inside the amoeba. 

However, everything sounds like it acts like an ordinary virus.  No life outside of the host.  Once inside of the host, it builds more viruses, and eventually lyses the host, spreading more virus particles.

When one considers viruses, there are several major categories of viruses, DNA, RNA, single stranded, double stranded, reverse transcribing, etc. 

Is there any overlap between many DNA and RNA viruses? 

Perhaps each major category of virus should be placed on its own separate genetic tree. CliffordK, Fri, 27th Dec 2013

Thinking about this some more.
Any organism travels to a place it can find food.
Eats the food.
Hunts for more food.

From yor_on's link:

It almost sounds like the virus is devouring the amoeba from the inside.

At the point where the amoeba is lysed, how much amoeba DNA is left?  Has the virus essentially eaten all of the amoeba DNA?  What about other Amoeba proteins?

So, perhaps this is a form of acellular life that devours cellular life.  Other viruses are supposed to take over the cellular mechanisms.  Does this one for the most part simply eat the cells?

Ok, it does apparently depend on at least some of the cellular mechanisms as notes indicate that they do not have any genes for protein translation.  I'm not seeing a lot of notes, but presumably they depend on their host proteins to also at least initiate transcription and replication.
CliffordK, Fri, 27th Dec 2013

I vaguely remember experiments in where they had worms eating worms, suggesting that they incorporated genes from it? But I'm pretty sure that one got debunked. And I don't know what mechanism may release the gene material they already store either? A catastrophe, changing the environment triggering a release of genes, would that be possible for example?

That one should be possible to test for in a lab environment I think? yor_on, Sat, 28th Dec 2013

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