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In a message dated 96-08-22 04:35:46 EDT, you write:

> Unfortunately, these are obligate parasites that have lost a large
>  part of their native metabolism.  Thus this does not show that free-
>  living forms could survive at this size.

I  just checked my microbiology text book and found that there is at least on
species of Rickettsia that can be cultured  on the outside of  of a cell
culture as opposed to inside and the authors made some phylogenetic
inferences based on this. There is another genus called Chlamydia that are
all totally obligate intracellular parasites <sic> and have lost even more
independent functions than Rickettsia. According to the authors, they clade
out differently  and are only if at all very remotely related. Both bacteria
are ~.1 -.3 microns big and are the smallest microbes known and rank in size
to some of the largest viruses known  which is what I find interesting since
they act like a virus by hijacking the host cells machinery!

Food for thought....

Thomas R.  Lipka
Paleontological/Geological Studies