From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Fri Dec 20 2002 - 13:22:08 MST
On Fri, 20 Dec 2002, Rafal Smigrodzki wrote:
> John Clark wrote:
> > "Rafal Smigrodzki" <rms2g@virginia.edu> Wrote:
> > >We don't know how long it takes to evolve highly
> > >radiation-resistant spores,
It may be important to keep in mind that D. radiodurans is
radiation resistant in a non-spore form. I haven't studied
the radiation resistance of spores -- I believe it is higher
than bacteria from which spores are derived but may not be
as high as D. radiodurans.
> > I don't know if Panspermia is true or not but the fact that a
> > bacteria like Deinococcus radiodurans exists is very puzzling.
Exactly -- that is one of the reasons I was so very interested in
studying it (circa 1991) and made a visit to LLNL telling them that
they should sequence it (circa 1993).
> > Why would Evolution go to all the trouble to provide that much
> > protection against a threat it is unlikely to ever see? Perhaps the
> > radiation protection is just a byproduct of something else
>
> That would be my guess as well.
> Rafal
This is the current working hypothesis of the people working
on D.r. They think that the radiation resistance is a byproduct
of dessication resistance. I.e. the organism has evolved to be
resistant to drying out -- something that one can view as being
much more common than high radiation doses.
But -- if the organism evolved to be dessication resistant then
that promotes the panspermia perspective since that property
certianly increases the transfer of the organism and/or the
information that may be contained in its genome.
Though I would need to look at the most recent data, I do believe
that D.r. is near the base of the evolutionary tree. It is also
very hard to mutate its genome (this creates some big problems in
studying it) so it is likely that any programs that compute the
evolutionary history of organisms based on the "typical rates"
will get it wrong with respect to D.r. So D.r. may be lower in
the tree than programs will currently estimate.
Mind you there are some other bacteria which have radiation
resistance and they are worth studying as well.
Why did I develop this high interest in radiation resistance?
Radiation exposure mutates cells and mimics many of the effects
of aging. Dr. L. Obukhova had a very interesting method of
exposing mice to radiation where just the head was irradiated
and guess what -- I saw mice that were perfectly healthy but
all of the hair on their heads was grey.
One only has to observe something like this once to be convinced
that "aging" is closely tied to DNA mutations (in part caused by
radiation but likely to more frequently be caused by free radical
damage [IMO]).
Robert
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