Purely a figment of your imagination

What amuses, annoys, concerns or otherwise interests me – Noodlemaz

New life, Jim? Not as we know it.

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The media has jumped on this one with gusto!

Craig Venter is at it again. To be clear, he’s been researching the idea of the ‘minimal genome‘ for years. It’s something lots of geneticists and microbiologists (along with many others, I’m sure) have been interested in since we started to understand DNA.

The minimal genome

So what is this? It’s the absolute smallest amount of DNA you need to make a cell that works. An organism. The ‘simplest’ (though I don’t like to call them that, really) organisms we see are bacteria and of these, Mycoplasmas have the least DNA.

So it ain’t the size, it’s what ya do with it that counts

The bacterial genus  with the tiniest genomes are the Mycoplasmas (when it comes to single-celled organisms, the idea of species doesn’t hold up too well but we can run with it). They’re really small. M. genitalium has only 582,970 As, Cs, Ts and Gs (the DNA building block molecules, base pairs, that make up the genome), which corresponds to only 521 genes and 482 proteins; the molecules that make up the majority of the cell and perform functions. Compare that with mankind’s approx. 23,000 protein-coding genes, made up of >3 billion base pairs.

Indeed, Venter’s lab filed patents for a minimal genome (that of Mycoplasma laboratorium!) back in 2006 – another contentious subject.

It was interesting when the M. genitalia genome was fully characterised because for the first time, we saw what was necessary to make the smallest known cells work. However, it’s still not the full answer, because maybe even this tiny bactierum still has genes and ‘junk DNA’ left over from a time when it was a bit more worldly…

Advantages of being a bug of the world

Mycobacterium leprae

Now I wish I had some slide images from my university microbiology course. To digress a little, a fascinating thing about bacterial evolution is that there seems to be a kind of progression they take – from living somewhere in the open (a diverse range of environments requiring loads of genes to utilise various food sources, evade many predators etc.) to living in a really specific niche.

For example Mycobacterium leprae is another teeny genome possessor, which lives only inside cells and has long been held up as an example of the most difficult thing to study (only possible to culture in armadillo footpads for some time, but I don’t know if this has changed). This one causes leprosy, if you didn’t guess from the name.

So when a bacterium ends up living only in one place, a very specific, isolated place at that – many of its genes become redundant over the generations, its genome shrinks as useless information is lost and also it doesn’t meet any other bacteria any more.

I saw an erroneous comment fearing that ‘synthetic bacteria might mate with natural bacteria’ – well, that’s not how they reproduce, but bacterial sex does exist; it’s just exchanging genetic information, rather than procreating.

Lust for Life

So when bacteria are cut off from the rest of the universe, inside the host organism deep within cells, they fester away – no new information coming in, very slowly dying off. Leprosy hopefully won’t be with us for much longer, it seems to be on its way out.

So the point of that digression; the Mycobacteria have been helping us understand what kind of genes are absolutely necessary for life because as their genome shrinks over time, only the most basic genes are passed on, the unnecessary extras disappearing in a kind of evolutionary fall-out.

Venter’s work has been in this vein; let’s see which genes we can slap together to get a functional cell out at the end.

Despite media shouting about the creation of synthetic life!!!, that’s not really what’s happened here. Venter has looked at a little bacterial genome, got some machines to make a copy of it and stuck it into a cell ‘shell’ that’s had all the genetic information taken out of it; the manufactured genome has then taken over control of the cell and this is their new ‘synthetic’ bacterium.

Talbot on BBC HYS put it quite nicely:

What Dr Ventner [sic] has done is the biological equivalent of typing the words from a book into a word-processor and printing it out again – then calling it a new book..!

It is an important advance, it is fascinating and it will lead to cool, useful things, but it isn’t the beginning of the apocalypse like many commenters would have us believe.

Do read Gimpy on some of the implications and mad press speculation and listen to Sir Paul Nurse on the subject on Radio 4.

Edit: via one of my colleagues, here’s a Skype interview with Craig Venter himself, explaining the findings.


Author: noodlemaz

I prefer to think of myself as a realist rather than a pessimist, but perhaps that's just optimistic. Honest, atheist, scientist, feminist.

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