posted on Aug, 31 2012 @ 11:42 AM
So I’m gonna discuss something I find particularly fascinating. Probably because I’m gross and like growing things on petri-dishes. So
microbiology has become a massive interest for me within the university course I’m studying. But I found out something particularly interesting that
could, potentially, make us rethink everything we’ve thought about viruses so far. And I like when things aren’t straight forward. So let’s get
In 1992, there was a particularly nasty outbreak of pneumonia in Bradford, England. Looking for the cause, they found an amoeba growing in a water
tower. This amoeba was Acanthamoeba polyphaga and was believed to be a gram-positive bacterium after initial gram staining techniques. They
named it (pretty unimaginatively) Bradfordcoccus and shoved it in a fridge.
In 2003, the sample was sent to the Université de la Méditerranée in Marsielle which is one of the greatest microbiology research centres in the
world and they did some tests. Mainly, they put some RNA to join to the bacterium.
And they found that it wasn’t a bacterium.
It was, in fact, a virus. The biggest virus any one had ever come across. The fella who found it named it ‘Mimi’, short for mimicking virus –
for its bacteria-impersonating properties - (and in homage to the name of a bacterium that his father told him a story about when he was a kid).
Now, Mimi is fairly complex. Okay, very complex. The biggest virus we’d ever found until 2010 when Mamavirus took that crown, and still the
See, we think of viruses as something simple. The infection mechanism is impressive, but viruses aren’t what we class as ‘alive’.
(Classification of life is something along the lines of MRS GREN as popularly taught in early education; movement, respiration, sensitivity, growth,
reproduction, excretion and nutrition)).They have to infect something else in order to reproduce themselves, can move but they’re lacking the
respiration, nutrition, excretion parts and therefore aren’t classed as ‘alive’.
So I said Mimi was huge, but let’s put it in context. The rhinovirus, which gives you that cold that you might be snuffling away on right
now, is around 30nm in diameter. So is poliovirus. Varicella zoster virus, the thing that gave you chickenpox as a kid (or as an adult
if you were really unlucky) is 150-200nm in diameter. H1N1, the virus everyone is terrified of at the moment is around 120nm. And human
immunodeficiency virus is also about 120nm. These are classed as large for a virus. (Consider a nanometre is 10^-9 of a metre)
So think about Mimi again. Because this virus has a capsid of 400-500nm in diameter, with fibres spreading out from it extending 750nm. She’s a
Mimi has around 1.2million base pairs in a double stranded genome. Polio’s genome is 7500 nucleotides. We managed to decode the genome and found
potentially 911 sequences that could code for proteins. Human influenza codes 11. For a virus, she’s incredible.
But it doesn’t even stop there because there were proteins in there that we were interested in due to similarities to genomes we could recognise.
Mimi has genes that relate to translation, metabolic pathways, DNA repair and protein folding. All of the kind of things you would expect in a living
organism. Mimi still lacks ribosomes and therefore needs a host to carry out translation, but the genes are there and she’s caused a lot of
excitement. Because we could have an indication that this virus is alive. And that could change microbiology as we know it.
Now, woah, we’ll hold our horses here because it’s never been proven. In fact, no one really knows quite what to make of these viruses. Maybe the
virus simply picked the genes up from horizontal gene transfer in the past or maybe it lost some genes when it became host-dependent. Just the fact
they’re there is incredible enough.
That’s not all, though. Because Mimi (and Mama) have other indications of life. In 2008 something else was discovered inside an Acanthamoeba.
Roughly 50nm long and multiplying in amoebas where the Mamavirus (the newly crowned biggest virus in the world) was present, step up Sputnik.
The first satellite virophage ever discovered.
Virophage literally means ‘virus’ and ‘eat’. This virophage is basically preying upon another virus in order to reproduce. Sputnik gets inside
the Mamavirus, hijacks the proteins and translates itself whilst at the same time causing Mama to produce ineffective copies of itself and preventing
death of the amoeba.
Everything is in a state of balance in life. Or at least it should be. We, as humans, upset this balance by being ‘clever’ (or destructive?) and
changing our surroundings to suit us rather than the other way around. The best theory scientists have to explain this is as follows.
But imagine this didn’t occur and we had a normal food chain of plant < herbivore < carnivore. Now, if there are a lot of plants, the herbivores
will move in and eat the plants and the balance will be restored. If there are a lot of herbivores and they’re eating off the plants, they’ll die
but so will the plants. So the carnivores come along to eat the herbivores. Too many carnivores and the herbivore numbers are kept down but the
carnivores will also starve; but this is good for the plants. Etc.
Now, starvation isn’t the only reason for death. Disease is also prevalent. So bacteria can affect plant numbers, herbivore numbers and carnivore
numbers, causing weakness and death by natural selection. But this can mean bacteria numbers are overgrown and they’re not as easy to kill –
living off little and possessing the ability to survive harsh conditions and adapt and reproduce quickly.
And so along comes the bacteriaphage virus, and this keeps down some of the numbers of bacteria by hijacking it to reproduce numbers of itself. But
then, if there are too many viruses, something needs to be introduced naturally (not by Dettol) to kill the virus, and what better than a virophage?
Now this doesn’t answer the question of whether or not this makes a virus more living than we have previously believed.
The lack of metabolism is what first caused scientists to think they weren’t, but defining ‘alive’ is a lot harder than the simple thing
that’s taught in school. We can see things as alive that may lack one or two of the characteristics and things as dead that may possess some. So
this complicates things.
Viruses can evolve (look at colds and flu – they change on at least a yearly basis. Remember, you can’t catch the same cold twice, but how many
people have experienced more than one in a single winter?) and passing on their genetic information to offspring plays a major part in evolution. Now
how many things that aren’t alive evolve? Just one? And that’s a virus.
But on the other hand, viruses could do none of the criteria for living without a host to bring it about.