[extropy-chat] What is the smallest genome possible?

[The Avantguardian]

--- John K Clark <jonkc at att.net> wrote:

> Robert Bradbury Wrote:
> 
> > As at least one virus has recently been found with
> a multi-thousand base
> > genome so I think the virus and bacteria
> definitions are starting to get
> > very fuzzy.
> 
> I disagree, the distinction between a bacterium
> (thank you Damien) and a
> virus (if virii or viri is a real word it damn well
> shouldn't be) isn't the
> size of its genome, it's the fact that a bacterium
> has a metabolism while a
> virus does not.

For the sake of thread discipline, I have moved the
grammatical discussuion to a separate thread. However
this topic is an interesting one. I agree that a
metabolism AND a genome distinguish bacteria from
viruses that have only a genome. However, Robert's
point is still valid.

There are things called mycoplasmas that dwell in a
twilight world between viruses and bacteria. They have
circular genomes and some housekeeping genes, yet are
obligate parasites incapable of living outside of a
host cell. They also share a plasma membrane with
bacteria but lack a cell wall. And they have tiny
genomes compared to bacteria. 

So the question remains: Are they viruses that evolved
plasma membranes, parasitic bacteria that got lazy and
ditched most of their genes, or simply a thing unto
themeselves?

On the other hand theer are viruses like herpes
viruses (including CMV, EBV, and others)that have
genomes in excess of 150kb (kilobases not kilobytes).
Amazingly the genomes of some herpes viruses include
counterfeit copies of human MHC genes (the id
mechanism of self for the immune system) that actually
fool the host defenses into "thinking" a cell is not
infected. 

> However I agree with you that it
> might sometimes become a
> little difficult deciding if something is a
> organelle or a bacterium. 
> gets even worse, a mitochondria cannot live unless
> it is imbedded deep
> inside another creature, but then neither can a
> tapeworm. When a organism
> evolves into a parasite or symbiote it always
> becomes simpler.

It has a whole becomes simpler, but the genes it keeps
should remain as highly derived as the free living
counterpart. That's my story at any rate and I am
sticking with it. ;)
 

Stuart LaForge
alt email: stuart"AT"ucla.edu

"More persons, on the whole, are humbugged by believing in nothing, than by believing too much."

- P. T. Barnum

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