Text 1149, 91 rader
Skriven 2004-12-21 22:08:00 av Larry Moran (1:278/230)
Ärende: Re: Biochemical evolution
=================================


On Mon, 20 Dec 2004 21:39:01 +0000 (UTC), 
Paul Ciszek <nospam@nospam.com> wrote:
> In article <cpt9hl$tc1$1@darwin.ediacara.org>,
> Larry Moran <lamoran@bioinfo.med.utoronto.ca> wrote:
>>On Thu, 16 Dec 2004 16:23:52 +0000 (UTC), 
>>Paul Ciszek <nospam@nospam.com> wrote:
>>> 
>>> I am not a biologist, but Archea show far more fundamental variation in
>>> chemistry than Bacteria or Eukaria, both in the types of chemical reactions
>>> they can cause and/or exploit, and in the substances that they are made
>>> of.  
>>
>>I don't think this is correct. Archaebacteria have a fairly limited
repertoire 
>>of the basic biochemical pathways. The other bacteria consist of species that
>>have a much wider variation in pathways. This includes most of the pathways
>>and enzymes found in archaebacteria *plus* lots of additional enzymes.
> 
> Well, I was refering to the fact that:
> 
> A) The archaea are sometimes made out of molecules that other types of
>    cells don't use.  Supposedly some of them use the left-handed forms
>    of certain molecules of which only the right-handed form is seen in
>    the other two domains, and the ones that live at extreme temperatures
>    have to use different proteins than other life forms or they would cook.

I'm not sure what you're referring to when you talk about the handeness of
molecules. Could you be more specific? The only example I know of is the
linkage in some glycerol lipids. It's a pretty minor difference and, in any
case, it doesn't relate to "diversity" since all archaebacteria have exactly
the same linkage.

There are thermophilic archaebacteria and there are thermophiles that are not
archaebacteria. All bacteria that live at high temperatures have adaptations
that allow their proteins to function without denaturing. Most (all?) of the
extreme thermophiles - those that live at temperatures >90 degrees - are 
archaebacteria. As far as I know those extreme thermophiles don't have
different genes than their non-thermophilic relatives.

I still think that diversity among archaebacteria is less than that among
the other bacteria.

> B) They can "feed" off of a greater variety of chemical reactions than
>    other living things.  (Are all chemotrophs archaea?)  Some "eat" the
>    iron out of shipwrecks, leading to anomalies like the tools recovered
>    from the Titanic, where the wooden handles were preserved by the cold
>    and lack of oxygen, while the iron had been eaten away by archaebacteria.
>    Others are found only in the tailings ponds of uranium mines.  One type
>    has been found living in nuclear reactors.

Most of the chemoautrophs are NOT archaebacteria. They tend to be related
to gram-negative proteobacteria although many are gram-positive species. 
There is more diversity among "eubacteria" than among archaebacteria in 
terms of the energy source.

As far as I know there are no archaebacteria that can use reduced iron as
an energy source. All of the "iron-eating" bacteria are proteobacteria and 
these are definitely "eubacteria."

The species that grows in mine tailings and industrial waste sites is 
Rhodococcus sp. - these are eubacterial species, not archaebacteria.

The bacteria that grow in the water core of nuclear reactors is Deinococcus
radiodurans. It is a "eubacterium", not an archaebacterium.

I'm afraid your opinion about the "diversity" of archaebacteria has been
influenced by false information.

>>Archaebacteria don't do photosynthesis. Other bacteria do it in many
different
>>ways including the full-blown version that was passed to eukaryoties. This
> 
> Do other bacteria do chemosynthesis?

I'm not sure what you mean by "chemosynthesis." Could you rephrase the
question?
There are lots of bacteria that can derive energy from inorganic substances.
Most of these are NOT archaebacteria. Is that what you meant?



Larry Moran
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