Eukaryotes are derived from prokaryotes. This is demonstrated by the fact that eukaryotic endosymbionts are derived from prokaryotes. Opponents to this have objected that such a transition must have left intermediary organisms, the lack of which strongly weakened this possibility.
Such an organism has in fact been discovered. Yamaguchi et al., J. Electron Microscopy (2012) report the identification from deep see survey of an organism with features that appear to be intermediary between prokaryotes and eukaryotes. This organism, named "Parakaryon myojinensis" for its intermediary location, is big, >100 times bigger than your usual prokaryote like E. coli. Its genome is composed of naked DNA fibers, instead of the classical eukaryotic chromosomes, and is surrounded by a single membrane instead of the classical double (single folded) membrane of eukaryotes. It also harbor various endosymbionts but no mitochondria. Thus, this organism appear neither to classify as eukaryote or prokaryote, but more like something in between.
The study is far from definitive. Indeed, there is no molecular identification of domain markers, like ribosomal RNA, or proteome oriented studies, most likely because of the lack of isolation and cultivation of this organism.
However, this is another example of the value of sampling the biodiversity that is out there.
Interesting article and I am looking forward to read more about this thought-provoking organism.
Such an organism has in fact been discovered. Yamaguchi et al., J. Electron Microscopy (2012) report the identification from deep see survey of an organism with features that appear to be intermediary between prokaryotes and eukaryotes. This organism, named "Parakaryon myojinensis" for its intermediary location, is big, >100 times bigger than your usual prokaryote like E. coli. Its genome is composed of naked DNA fibers, instead of the classical eukaryotic chromosomes, and is surrounded by a single membrane instead of the classical double (single folded) membrane of eukaryotes. It also harbor various endosymbionts but no mitochondria. Thus, this organism appear neither to classify as eukaryote or prokaryote, but more like something in between.
The study is far from definitive. Indeed, there is no molecular identification of domain markers, like ribosomal RNA, or proteome oriented studies, most likely because of the lack of isolation and cultivation of this organism.
However, this is another example of the value of sampling the biodiversity that is out there.
Interesting article and I am looking forward to read more about this thought-provoking organism.
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