Jurassic park lecture

Bryan L. Ford fordb at bcc.orst.edu
Thu Mar 13 22:12:03 EST 1997

Anthonie Muller wrote:
> On 4 Mar 1997, Ed Rybicki wrote:
> > > From:          Anthonie Muller <awjm at holyrood.ed.ac.uk>
> > > When I read all this talk about DNA conservation in amber, I must always
> > > think about H.J.Dombrowski, who  claimed to have isolated bacteria from
> > > old salt deposits (see for instance Umschau 23 (1965) 736-736). It seems
> > > to me that a high salt concentration may very well protect against all
> > > kind of degrading effects.
> > > Why is his work ignored? Have I missed an obvious counterargument?
> >

I am pleased to see the continuation of this thread and the thoughtful
comments it is generating. I have not looked up any of the Dombrowski
articles, but it seems that these halophiles may be alive and well in
the salt, or at least within a dormant spore which can regenerate the
bacterium when sufficient water happens along. Isn't this substantially
different from the amber-entombed bacteria? Since they arguably have no
likelihood of returning to a bee's gut once they are released by some
accident of geology. So that in amber we have a truly fortuitous
situation only incidently relying on the storage properties of the amber
and the durability of the spores formed, compared to a normal functional
aspect of the halophile's adaptation to the vicissitudes of its saline
environment, including periodic dessications.

> I can imagine that radioactivity (C14) of DNA constituent atoms may
> destabilize a genome, but nevertheless self-repair mechanisms do exist.

This is an interesting speculation, but I think it would falter from
insignificance, since (by a quick calculation) carbon 14 in living
aerobic tissues is about one part in 10 to the 12th of the most abundant
(carbon 12) isotope-- and of course after 10 half-lives (10 X 5730 or
57,300 years) the abundance would be over 1000 times lower. 

> Determination of the amount of radioactive isotopes in a bacterium by
> massaspectroscopy might by the way be a method to proof an old age.

And again there is this unfortunate limit to the usefulness of 14C due
to its 5730 year half life. Even the best mass specs presently "lose it"
at something like 50,000 years. But this does not preclude some other
clever use of other radioisotopes for dating. 

> In Scientific American of a few months (?) ago there was  an article about
> bacteria deep underground, in natural water. The bacteria were
> supposed to have been there since geological times, and the bacteria were
> supposed to be not very active. If their metabolic activity is very low,
> the instability of their DNA should also be a problem. So, again, why
> discriminate against salt bacteria?

Here again, we are talking about bacteria that naturally live in such a
niche.... they are apparently quite alive, but with extremely low
doubling rates and so on. I would say that this is not really
qualitatively similar to the critters seen in Raul Cano's heroic
recoveries from amber. In regards to DNA repair processes in
subterranean prokaryotes, it would be interesting to know the level of
ionizing radiative flux experienced by organisms at such great depths.
My guess is that the level is very low because of in situ shielding
(dense material in the earth's crust) even though on a volumetric basis 
radioactive decay processes are probably at a high level.


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