Sunday, March 02, 2008

Addiction and Revenge in the Microbe World

One of the fastest ways to get me to roll my eyes is to say something along the lines of 'But viruses arent ALIVE!!!' 'Alive' is an archaic, unhelpful word when looking at evolution and the Tree of Life.

Viruses/RNA/Prions ≠ rocks. Dont be dumb. *rolleyes*


So I flipped out last week in class when we learned about a cool trick plasmids can play-- Plasmid addiction. Why is there not a Wikipedia page on this topic for me to link to?? Theres not even another blog around thats posted on it! BUT ITS SO COOL!!

That horizontal gene transfer that some people get so pumped about? It can be mediated by plasmids-- an easy example is how antibiotic resistance spreads between totally different kinds of bacteria. Some plasmids (even though they arent ALIVE!!) have evolved a a sweet system for ensuring their propagation a la 'The Selfish Gene'/'Dune'-- Plasmid addiction.

Some plasmids encode for:

  1. a poison
  2. the antidote
As long as the bacteria keeps the plasmid around, everything is fine! Even though the poison is always being made, there is always tons of antidote around too. Its a burden to the bacteria, but the poison has no effect.

But if the bacteria says 'Ugh. Im not wasting any more resources making this damn plasmid. Lazy bum. Im kicking him out' the plasmid pulls, like, a 'Kill Bill'-esque revenge plot. The poison has a longer half-life than the antidote. If the plasmid is no longer there to encode the antidote, all the left-over antidote degrades, and the poison is left to kill the bacteria.

That. Is. AWESOME.


Dunc said...

Huh. Microbiology is twisted.

I wonder if you could convince bacteria to evict their addictive plasmids, so they croak when they go cold turkey.

Or if noncoding dna in bigger organisms can pull similar tricks.

Dan said...

But, viruses can't drive, vote or play Guitar Hero!!!!

(eyes rolling yet?)

Anywho, the reason why the Plasmid Addiction page doesn't exist is because you've not written it yet. Get on it! It's not like you're busy or anythi... umm...

Put the knife down. We're all friends here.

The Factician said...

The next twist will blow your mind...

Some of those addiction modules are also found on chromosomes. What the hell for? You don't need an extra level of selection to maintain a chromosome...

Ron said...

You mean a page like this?

Or are you talking about a different system?

Ian said...

Wow - that is really cool.

Dodging tornadoes?

Aaron Golas said...

Holy crap, that is awesome! I've read about cost-compensatory mutations for plasmid-bound antibiotic resistance, but this is an entirely different trick for keeping a plasmid around.

Factician, that is an interesting twist, but I can't say I'm entirely surprised. If you incorporate the addiction module into your chromosome, you're free to ditch those deadbeat plasmids!

Dunc said...

"The next twist will blow your mind...

Some of those addiction modules are also found on chromosomes. What the hell for? You don't need an extra level of selection to maintain a chromosome..."

Maybe to keep the chromosomes around during those heady days when sexual reproduction was evolving or developing, so uncool bacteria couldn't just say 'screw this sex thing' and go back to fission? <_<

Tyler DiPietro said...

Neat stuff.

I've never been able to shake the idea that talking about "living" and "non-living" as discrete categories is irreparably misleading. At the very least, you're talking about a continuity.

It also seems to give the impression that there is some kind of fundamental essence separating living and non-living systems, which feeds into elan vital fallacy. In my experience, it's that kind of intuition is the biggest barrier to getting people to shake creationism.

D. Cardinale said...

Wow, that's interesting as hell. I'd love to learn more about the presence of addiction molecules on chromosomes, though.

Bob O'Hara said...

Factician, don't leave us hanging like this - tell us more!

My first guess for explaining that would be meiotic drive.

I love the rather Baroque nature of biology, especially the way it continues all the way down to the DNA. It's almost as if it's been cobbled together with no fore-thought.

Qzerty said...

The world would totally be a better place if "The Selfish Gene" were required reading in highschool. Or SAT passages. Or SOMEWHERE. I first read it in a handout a poli sci class.

/changed my life.

S_A_Wells said...

That's... elegant, vicious, and highly evolvable.

Reminds me of my favourite Kill Bill variant joke: "Fear my five-point palm technique. I prod you in five places, and forty years later you die in a nursing home."

The Factician said...

tell us more

I think the latest thought on the chromosomal addiction modules is that they're regulatory elements. When expressed at low levels the "toxin" is a protein inhibitor (with a particular target) and the "antitoxin" is an anti-inhibitor, that together allow the cell to toggle the protein activity. Plasmids have hijacked these systems, and express them at *much* higher levels.

But there's a woman in Israel (Hanna Engleberg-Kulka) who thinks that the chromosomal versions are regulatable suicide modules, whereby starving bacteria can intentionally kill off a small proportion of their own population, to provide metabolites for the remaining cells. When she first proposed this in the late 90s it was a pretty popular hypothesis, but I don't think many people think this is true any more.

Anyway, put Ken Gerdes (I forget which Scandinavian country he's from) into PubMed, or Hanna Engleberg-Kulka. Those are the two labs that have done most of the heavy lifting in this area.

Chipmunk84 said...

Check out stellate and supressor of stellate in drosophila! If that isn't a beautiful example of design (don't worry, I'm being sarcastic), then I don't know what it. There's also a similar-ish explanation for uniparental inheritance of mitochondria and the evolution of sexes. Have a look at"Selfish genetic elements and their role in evolution: the evolution of sex and some of what that entails". It's an old paper but intragenomic conflict is interesting to say the least.

Janiece Murphy said...

Abby, your passion for science is made of the teh Awesome. And gives me hope!

And plasmid addiction. Cool.

Antonio Mas said...

If you put Rafael Giraldo at PubMed, you will see a lot of information about kis/kid system.

Aaron Golas said...

Alright, looks like I have some papers to look up if I get some free time. Thanks!

Torbjörn said...

That is cool.

Viruses/RNA/Prions ≠ rocks.

Sorry, I'm not buying that outright.

Ever since a commenter put me onto this definition of organisms, I've slept easier:

An organism is the unit element of a continuous lineage with an individual evolutionary history.

Defining anything participating in an evolutionary process as life consistent with making the process itself the adjudicator is reasonable. Now, I wouldn't worry about my status as individual as not being "fully alive" as opposed to a sufficiently large population - put me next to a sweet and willing female, and I would make my best effort making life. :-P

But "prions" doesn't seem to have much of an evolutionary history. AFAIU the disease form of protein folding (or whatever) can jump the species barrier, but can the folding evolve to use radically different substrates and environments? IMHO it is the prion protein that clearly evolves, and it has no individual lineage.

Incidentally I think the above definition nicely conform to Tyler's observation. The hereditary properties of an evolutionary system can AFAIU be distributed (ERV's quasi-species viruses, for example) and is interacting with the properties of the environment. Room for as much continuity that one can wish for (or observe, rather).

Gary said...

That is so cool.

This is one of the reasons I read your blog.

Torbjörn said...

Seems I was wrong about the pathological conformation not being evolving, and independently, as already the next post explains.

Life is a fascinating process!

mcmillan said...

That's is really friggin cool. Thanks for telling us about this. I'm disappointed it hadn't come up in any of my classes before

jane said...

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