Posts Tagged ‘life’

Big viruses have little viruses….

28 August, 2008

Just when you’d heard of mimiviruses, and thought it couldn’t get any stranger…the same team now bring you “mamavirus“, so named because it’s bigger!

But wait, that’s not all: apparently the new viruses have their very own “virophages” – smaller viruses which parasitise mamavirus-infected cells, and so called because they look like and have homology to bacteriophages.

And that’s still not all…Helen Pearson in the 6th August online Nature News then makes a case for viruses being considered as being alive, on the strength of this parasitism – and its detrimental effect on the larger virus, in terms of aberrant assembly, lower yield in infected cells, and so on.

Well, now…some of us have never thought otherwise, have we?  And despite all of the hype about how huge these viruses are, and how they blur the boundary between alive and dead – they don’t do they?  For all their complexity, mimi- and presumbably mamaviruses do exactly what all other viruses do: they obligately parasitise cellular organisms, and use their machinery (and especially ribosomes) to make viral components which asemble into particles.

And the news piece goes on:

“The discovery of a giant virus that falls ill through infection by another virus is fuelling the debate about whether viruses are alive.

“There’s no doubt this is a living organism,” says Jean-Michel Claverie, a virologist at the the CNRS UPR laboratories in Marseilles, part of France’s basic-research agency. “The fact that it can get sick makes it more alive.””

Ye-e-e-ssss?  Really?  And calling what is obviously a satellite virus – for all that it is a big satellite virus – a “virophage” is simply creating new terms where none are necessary.  Actually, they go one worse than that: the original article refers to the satellite as “Sputnik” throughout, in a breathtaking display of artistic licence.

But putting the outraged taxonomist in me aside, this is a truly amazing discovery, worth all of the hype: it shows that we really don’t know a lot about what is sitting in plain sight – in cooling tower water, in this case – let alone what is is sitting in deep oceans, in terms of viral biodiversity.

While the mamavirus is interesting enough, what should be called Mamavirus associated satellite virus rather than Sputnik, is even more so: satellite viruses are generally small and have very few genes, whereas this has 21 genes in a ~18 kb circular dsDNA genome, makes isometric particles 50 nm in size (which can be found within mamavirus particles), and in the words of La Scola et al.:

“…contains genes that are linked to viruses infecting each of the three domains of life Eukarya, Archaea and Bacteria. Of the 21 predicted protein-coding genes, eight encode proteins with detectable homologues, including three proteins apparently derived from APMV [Acanthamoeba polyphaga mimivirus], a homologue of an archaeal virus integrase, a predicted primase–helicase, a packaging ATPase with homologues in bacteriophages and eukaryotic viruses, a distant homologue of bacterial insertion sequence transposase DNA-binding subunit, and a Zn-ribbon protein. The closest homologues of the last four of these proteins were detected in the Global Ocean Survey environmental data set, suggesting that Sputnik represents a currently unknown family of viruses.  Considering its functional analogy with bacteriophages, we classify this virus as a virophage. The virophage could be a vehicle mediating lateral gene transfer between giant viruses.”

Fascinating indeed: this parasite upon a parasite – it replicates only in the “giant virus factory found in amoebae co-infected with APMV” – is bigger than many autonomous viruses infecting mammals, looks like it is at least partly derived from a bacterial virus in that it may integrate into its host (the mimivirus?) within a eukaryote, and may shuffle DNA around between other viruses.

I’m definitely working in the wrong field.

MicrobiologyBytes Archive

14 December, 2007

Before I established this site, I posted a number of guest blogs to do with viruses on Alan Cann’s very wonderful MicrobiologyBytes site. Here are links to all the virus-related ones.

Maybe Not Quite The End

Posted on January 15, 2008
Review of a paper describing the receptor for the H5N1 HA protein

Given the current scare over H5N1 influenza virus in swans in the UK, it is possibly timely to recall that I wrote a little while ago in MicrobiologyBytes about how easy it appeared to be for […]

Bandicoot Blues

Posted on November 30, 2007
Description of a unique newly-described virus that looks like a chimaera of a papillomavirus and a polyomavirus

Now that the dust has begun to settle after the launch of Merck’s much-hyped Gardasil genital papillomavirus vaccine – discussed in MicrobiologyBytes here and here – people are turning again to looking at the natural history […]

Hurting rather than helping?

Posted on November 21, 2007
Some news on the failure of the Merck Adenovirus 5-vectored HIV vaccine

It should not have escaped the eye of the interested bystander that there has been a most unfortunate and premature end to a HIV vaccine trial recently – and that something that had been tested as […]

A Deeper Meaning

Posted on November 10, 2007
Some microbiology-related poetry….

I inadvertently became a published literary critic a little while ago. A long-time English Department colleague asked me for some help interpreting the collected works of possibly the most important modern poet from South Africa, and […]

Don’t look now, they’re in your genes

Posted on September 14, 2007
Description of natural insertions of virus gene fragments into a variety of organisms and how they elicit pathogen-derived resistance

And they’re protecting you! If you’re an insect, that is. Or possibly a plant.
In a remarkable convergence of news, an Israeli group led by Ilan Sela described how Israeli acute paralysis virus, which is implicated in […]

To bee or not to bee

Posted on September 11, 2007
News of how a single virus is suspected in the causation of “colony collapse disorder” of bee hives in the USA

A major recent mystery in US agriculture has been the phenomenon of “colony collapse disorder” (CCD) in honey bees. […]

This is the End

Posted on August 29, 2007
H5N1 highly pathogenic avian influenza virus mutates…

This is the End. Or the beginning of the end. Or possibly, the end of the beginning?
To misquote the immortal Bill Shankly: “It’s not a matter of life and death: it’s much more important than that”.
Having […]

Rolling down the road

Posted on August 27, 2007
Musings on rolling circle replication in viruses

In my idle moments (alas, too few these days!) I often try to think up lists of rock songs with a virus theme: you know, like “Cucumo” by the Beech Boys… “I got them ol’ burnin’, […]

Rooting the tree

Posted on August 3, 2007
News on inferring “ancestor sequences” for HIV to help make broadly effective vaccines

While fossilized viruses have never been found, we can often infer probable lines of evolutionary descent by analysis of extant genomic sequences. This sort of molecular phylogenetic approach has thrown up all sorts of interesting […]

It’s Life, Jim, but not as we know it…

Posted on July 24, 2007
Exploring what it means to be “alive”

Which could well apply to viruses, my very own favourite organisms – after all, they don’t respire, grow, excrete or any of those other good things […]

A feeling for the molechism*

Posted on June 26, 2007
Musings on what viruses are.

I think it’s permissible, after working on your favourite virus for over 20 years, to develop some sort of feeling for it: you know, the kind of insight that isn’t […]

Plus ça change, plus c’est … le same Web, only better?

Posted on June 8, 2007
A personal history of teaching Virology via the Web.

My, how things do change… I found myself reflecting, while I was looking over the detritus on our Web server of some 13 years of posting pages on the Web. “Orphan” pages, unconnected […]