prokaryote evolution and globin proteins

B.J.Tindall bti at DSMZ.DE
Tue Oct 22 10:47:14 CDT 2002


Ken Kinman wrote:

At 03:59 22.10.2002 +0000, Ken Kinman wrote:
>Dear All,
>      It's been a couple of years since I've delved seriously into
>prokaryotic evolution, so maybe it is time I caught up a little.  It seems
>that myoglobin-type genes have been discovered in both eubacteria and
>metabacteria (aka "Archaebacteria").
>      SCIENTIFIC PREDICTION.  Workers at the University of Hawaii have
>concluded that such genes are ancient based on their discovery in
>Metabacteria.  However, I would go even further and predict that some
>cyanobacteria will contain the most primitive myoglobin genes of all, and
>that alpha and beta hemoglobin genes evolved separately in different
>bacterial lineages.  The genes for alpha or beta globin genes were then
>united by horizontal transfer to create hemoglobin.

Do you have a reference?

>     Whether this occurred in a cyanobacterium originally, or occurred in a
>eukaryote and transferred back to certain cyanobacteria is anybody's guess.
>In any case, the split between globin and chlorophyll genes is quite
>ancient.
>     And contrary to what the University of Hawaii scientists state,
>molecular oxygen was probably present 3.5 billion years ago.  Not in the
>atmosphere (where it would only accumulate much much later), but within the
>layers of stromatolites.  Photosynthesis is truly ancient, and the
>Metabacteria of present deep-sea vents are most likely tapping into the
>energy of ancient photosynthetic products that have been subducted and
>slowly being recycled

Well this assumes that photosynthesis always involves the production of
oxygen when water is split. The fact that water is split and not carbon
dioxide comes from the work of the bacteriologist van Niel. He was working
with organisms which oxidise sulphide via sulphur to sulphate. Since
sulphur is released from hydrogen sulphide he concluded that H2S and H2O
were analagous in their function i.e. H2O is split to give molecular
oxygen. ...and what has that to do with cyanobacteria? About 25 years ago
it was shown that there are cyanobacteria which can grow on sulphide and
that molecular oxygen was not always produced by cyanobacteria. The use of
sulphide is not uncommon among many of the modern "anoxygenic phototrophic
bacteria" and one could, of course suggest that similar sulphide based
photosynthesis occurred in ancient stromatolites.
Brian

>
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