Re: Bacteria in Nuclear Reactors

["Björn Cedervall" <bjorn_cedervall@hotmail.com>]

I could imagine that these bacteria which can tolerate unusually high 
dose rates actually evolved to tolerate other stress factors than 
radiation (like heat or chemically induced DNA damage). The RecA system 
for instance induces a whole bunch of proteins which includes repair 
enzymes as well as proteins that stimulate more incoming mutations (more 
misrepair). In other words - they have evolved for evolvability. I do 
not remember the sources I browsed through over the years - some may be 
found in Friedberg's book from 1985 (DNA repair). The radiation climate 
- say 2 billion years ago was certainly more radioactive (just count 
backwards on potassium 40, not to mention the Oklo phenomen (U235 etc)) 
but I still doubt that this was the main factor here (heat and UV are my 
major candidates). It seems more probable that radiation induces a 
general stress response (common signal pathway). A normal mammalian cell 
may have to handle up to perhaps 100.000 different DNA damages per day 
but a majority of these are base losses (guanine for instance) - if this 
is at 37 degrees centrigrades (spontaneous hydrolysis) - what could then 
not happen if bacteria thrive in water that is 80 degrees C or more? (I 
don't understand how the DNA is held together - must be strong protein 
structures).



"Food" - I think there is plenty of it (much of the periodic system). 
There are nice refs. on bacteria "out there" about bacteria living in 
extreme conditions - one article may have appeared in Sci. American some 
5-10 years ago (?). From there I recall some texts about porphyrin like 
molecules that oil drillers (?) found very deep down (order of 1 km??).



The builders of evolutionary history have to consider changing oxidative 
potential in the relevant environments.

Bjorn Cedervall

Karolinska Institutet

bjorn_cedervall@hotmail.com



>OK, I can accept the idea of bacteria that have adapted to high

>temperatures (especially in water) and to high pressures (deep sea

>conditions). I can even accept the idea of bacteria that have adapted 
to

>high radiation environments (although the evolutionary sequence where 
the

>bacteria encountered the high radiation fields isn't obvious to me).



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