Info req.: molecules/morphology

[Ken Kinman]

Brian,
     The main point that I was making is that it was premature to give a
formal name (much less two) to Xenarchaea (Korarchaeota).  I just threw in
my other opinion (about how distinctive it is) just because the opportunity
presented itself and to buttress up my argument a little further.  But I
examined the actual rDNA sequences of this group, while some of those who
think they are so much more distinctive may be relying on computer output
telling them how distinctive the group is.  It may sound old-fashioned to do
some analysis without a computer, but if one is going to prematurely name a
group like Xenarchaea, I would hope that they didn't do it just because
computer-generated trees said so.  Until more definitive evidence is
presented, or the rDNA sequences are analyzed more carefully, I will
continue to regard them as an unnamed Order of Class Crenarchaea (Phylum
Metabacteria/Archaebacteria).
    Thank goodness Hugenholtz and Pace call their distinctive eubacterial
groups "Candidate Divisions", because most of them seem to be popping up in
the parts of prokaryotic phylogenies most affected by Woesian misrooting,
and I suspect computer programs are exaggerating the distinctiveness of many
of those groups as well.  But they are not compounding the problem by giving
them formal names.
                        ------Ken Kinman
********************************************************
>Ken Kinman wrote:
> >     Both of these groups have been virtually based on the distinctive
>nature of their SSU rRNA only, but I think they were too slow to formally
>recognize the one, and have greatly overestimated the distinctiveness of
>the other.  Each case must be decided on its own merits, but in most cases,
>I would say it would be best to wait for morphological confirmation.  The
>Verrucomicrobium case was highly unusual.
>Brian Tindall responded:
>The problem is that we have members of the genus Verrucomicrobium and
>Prosthecobacter in pure culture, whereas we do not know much about the
>Korarchaeota. We can gather data on the first group and describe not only
>genetic differences (i.e. 16S rDNA sequences) but also phenotypic
>differences, whereas in the latter case we only have the 16S rDNA
>sequences. I confess that I find it rather premature to state that one has
>over estimated the significance of the Korarchaeota when one has little
>data in support of either point of view.
>Brian
>
>
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