pre-mitochondrial electron transport

James O. McInerney Ph.D. jamm at nhm.ac.uk
Wed Apr 17 08:47:24 EST 1996

Hi all,

	It has been pointed out to me by somebody here at the museum that the 
date for the mitochondrial endosymbiosis (or whatever you wish to call 
it) has continuously been pushed further down the eukaryotic tree (by 
unearthing evidence for secondary mitochondrial loss).

	Now, there is general agreement that the mitochondrion is monophyletic 
(descendent from the ancestors of Alpha proteobacteria).  Alpha 
proteobacteria are _relatively_ recent bacteria (as judged by molceular 
trees, and assuming a reasonable molecular clock), so mitochondrial 
eukaryotes can only have evolved _relatively_ recently.  Therefore, a 
HUGE length of time elapsed between the splitting of 'Eukarya' and 
Bacteria.  Sooo, in that time there must have been some eukaryotes that 
were successful.

My points are:

1.	Were the eukaryotes that survived for > 1,000,000,000 years, 
completely supplanted when the mitochondrion evolved? maybe it is a 
problem with our sampling of microeukaryote diversity (quite likely 
actually), maybe they WERE supplanted, maybe they didn't exist at all.

2.	From the energy point of view (hope my ignorance of bio. doesn't 
embarrass me here), if these primitively amitochondrial eukaryotes had  
good metabolic systems (they lived on their own for maybe a billion yrs, 
didn't they?), then these systems should surely be seen at least in some 
phylogenetic groups (one would think) today.  

	I guess the problem is that less than 100 genes are sequenced in 
Giardia, less than 30 in Trichomonas and not many genes from the others.  
Not many people are PCRing primitive eukaryotic 18S rRNA sequences from  
natural samples (not to the same extent that they are doing it for 
prokaryotes) and until then....

Dr. James O. McInerney Ph.D.        Phone/Voicemail: +44 171 938 9247
Senior Scientific Officer,          email:j.mcinerney at nhm.ac.uk
The Natural History Museum,         
Cromwell Road,
London SW7 5BD

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